In the popular consciousness, the Victorian era seems to be thought to have retained a static social, political, and cultural life, despite its 64 long years of duration. This is obviously no less absurd than thinking that American culture and politics remained unchanged in the period from FDR's inauguration in 1933 to the end of Bill Clinton's first presidential term in 1997 (a period just as long as Queen Victoria's reign).
To represent the temporal distances between different parts of the Victorian era in another way, the culture that produced the final chapters of Dickens' Oliver Twist in 1839 was clearly not the same culture that produced Bram Stoker's Dracula (1897), just as the culture that produced MGM's The Wizard of Oz (1939) was clearly not the same culture that produced The Big Lebowski (1998).
Therefore, I am deeply interested in understanding the political, social, and cultural shifts that differentiate the various sub-periods of the Victorian era in the land where its namesake "reign[ed] but [did] not rule."
The most major shift is likely the massive increase in the electoral franchise, and the wider impact that had on Britain's politics and cultural norms. It's worth accounting for the 'Great' Reform Act 1832, which roughly doubled the comparatively tiny electorate by allowing the lower-middle class the uniform ability to vote. Previously, constituencies had a variety of voting requirements, from commonsense ideas of being a local ratepayer/having a certain value freehold/leasehold, to antiquated tests such as having a hearth big enough to wallop a pot (literally, boil a cauldron). The GRA made it so that all (urban) boroughs, and all (rural) counties had the same requirements, and attempted to redistribute seats to account for industrial and population changes, particularly in the north (places like Manchester had not had their own MP previously). However, this so-called 'Great' Act was passed more to preserve the current system and gain political advantage for the Whigs, rather than an enlightened view of democracy, which remained a dirty word. As GRA champion Earl Grey (of tea fame) noted in the House of Lords, "The principle of my reform is to prevent the necessity for revolution, there is no one more dedicated against annual parliaments, universal suffrage and the secret ballot than I am."
(FYI, the parties' names change in this period, from Whig to Liberal, and from Tory to Conservatives)
The working-class were completely excluded from the GRA (in fact depending on what your constituency was beforehand, you might have lost the vote). This helped give rise to the Chartist movement of the 1830s-50s, pressuring for political reforms such as annual parliaments and universal (fe)male suffrage, and payment for MPs to account for working-class representation within Parliament. In short, this failed, however the idea was not killed. The 1867 Reform Act, this time passed by the Conservatives (future PM Disraeli opposed the Liberal's proposals, and then passed a more sweeping reform in an attempt to ingratiate the party with the new voters). This was then followed by the Secret Ballot Act 1872, and the Third Reform Act 1884 (this time passed by the Liberals). Combined, these acts went from 1 in 5 male adults having the vote to 3 in 5. Supporters of universal suffrage would have to wait until after WW1.
Clearly, the massive increase in the electorate in a relatively short period had predictable consequences like policies geared towards poorer voters etc. Whig and Conservative reforms of factories and mines in the 1830s/40s for example were carried out in part to try and satiate the bitter working class (largely successfully in my opinion). However, there are two areas which I think are more worth examining.
In terms of governmental sanitation, the UK government had been woefully lacklustre at the start of Victoria's reign. Government and charity reports had found that life expectancy and living conditions in the cities were appalling, but the government had little reason to act. The 1848 Public Health Act was largely optional, giving councils the power to inspect sewers for example, but no compulsion to. The increase in the electorate, combined with the growing acceptance of Louis Pasteur's Germ Theory of disease (1861), led to pressure to act. Therefore, the Public Health Act 1875 was much more stringent, compelling councils to have water and sewage inspectors, and requiring all new housing to have running water etc (though this was not fully adhered to). Therefore, political change had a significant impact on the incentives of the government to improve living conditions. By the end of Victoria's reign, governments began considering the welfare of its people as a key concern, the clearest example being shortly after with the National Insurance Act 1911.
Another area where there were unintended consequences was in Britain’s relationship with Ireland. Ireland was overwhelmingly Catholic during this period, yet Catholics were only giving equal rights in 1829. Even then, Wellington and the Tories had deliberately raised the property qualification disproportionately high in order to prevent a surge of Catholic votes. I do not wish to simply equate Catholicism with nationalism, but for the purposes of this answer just be aware there was a clear connection between the two during this period. There had been several attempts at rebellions, from the genuinely concerning 1798 with the failed help of Revolutionary France being the best example, to the woefully dismal 1848 ‘rebellion’ during the Famine which is also known as the Battle of Widow McCormack’s Cabbage Patch (summing up the rebellion pretty well). However, after the 1884 Reform Act, Ireland’s electorate skyrocketed. This led to the rise of the Irish Parliamentary Party, also known as the Home Rule Party. Its leader, (Protestant) Charles Stewart Parnell helped to pull off something which no-one had ever done before; convincing a sitting British PM that Ireland needed some form of self-governance (Home Rule). Gladstone and the Liberal Party proposed 2 Home Rule Bills (1886 and 1893), the latter passing the House of Commons, but was defeated by the Conservative-dominated Lords. This helped cause a resurgence of loyalism in Ireland, particularly in Protestant heartlands of Ulster and Dublin. These Ulster Unionists would, by the start of the 1910s, form the paramilitary group the Ulster Volunter Force (approx 100,000 men), prompting the creation of the nationalist Irish Volunteer Force (approx 80,000). In short, the Victorian period saw a radical change in the government’s relationship with Ireland, as well as increasingly radical, overt and violent demarcation between nationalists and loyalists, ultimately leading to civil war and partition in the early 1920s.
Hope this creates some divisions for you!
This is an interesting question, but it's impossible to answer due to the nature of all periodization - that is, it's only very relevant in one specific context. "Victorian" literally only means the time covered by Victoria's reign, just as "Edwardian" refers to Edward VII's reign and "Georgian" the reigns of the Hanoverian Georges. That's it: nothing but dates.
We can speak of the mores or the fashions or the popular literature of any of these periods, but in essence "Victorian popular literature" only means "literature that was popular at some time between 1837 and 1901". Any further periodization should really come about because you're discussing one subject and how it changes, because it will be irrelevant to just about any other subject that might be discussed under the same heading.
For instance, to use my own area of specialization, I could split the Victorian era into the pre-hoop era (1837-1855), the hoop era (1856-1869), and either the post-hoop era (1870-1901) or split that further into the first bustle period (1870-1875), the Natural Form era (1876-1882 - so-called because of the use of understructures to produce a pseudo-natural shape to the lower half of the body), the second bustle period (1883-1888), and the post-bustle period (1889-1901). Within fashion history, it's enormously useful to be able to say "during the Natural Form era ..." and have everyone know what dates I mean by that and to have a basic image of Natural Form dress in their minds. But if I were to take this periodization out of context and try to use it to better understand the nineteenth century as a whole, or Victorian art or literature, the fault lines would essentially be falling in random places. You could divide it up by stages of the Industrial Revolution, or the tenures of American presidents, or British prime ministers, and you have the same problem.
The real problem is that the popular consciousness does invest adjectives like "Victorian" with an extra meaning beyond the simple time span, and there's very little we can do about that except to write and talk about the years that fall within that period as they really were, and about the transformations that occurred through them.