How different were the colonists and the British during the American revolution? At that point, would they have had different accents? Were all of the British soldiers actually British people who came over on ships? Just wondering how far apart the cultures had grown at that point.

You've got a bunch of questions all slammed together, so I'll do my best to break them up into digestible chunks.

To answer the first part of your question, how different a given community was from Great Britain is going to vary hugely based on location, what non English people were living in the area (central PA had huge numbers of German immigrants, the Backcountry generally had huge numbers of Scots Irish, Enslaved west Africans nearer the coast, etc) so a wealthy white guy living in NYC could probably fit in were he in London, but a Scots Irish farmer on the frontier getting in on and off conflicts with Native people probably couldn't. Looking at accounts from British people coming to North America, regionalism is one of the key themes. My personal favorites are Nicholas Creswell and Phillip Vickers Fithian, both of whom describe regional variations in colonial culture from a British perspective. Fihian, for example, describes coastal Virginians as being very refined, loving fine clothes and dancing, and celebrating Christmas by firing their guns in the air. He describes Virginians west of the blue ridge as being incredibly warlike, writing “Mars, the great God of Battle, is now honored in every part of this spacious Colony, but here, every Presence is warlike, every Sound is martial.” for secondary sources on this, I recommend "A Revolutionary People at War."

Regarding accents the answer is yes, they were probably different, and the best resource on the subject is Kathy Hellier's "18th century English as a second language." She gets into regional and ethnic dialects, and most of her books come with a CD recording what she thinks they sounded like.

Regarding British soldiery, the answer is no, they were not all actually British. Massive numbers of loyalists enlisted to fight for the crown, many German principalities and states leased their armies to Great Britain to fight (these troops are erroneously referred to as "Hessians" even though many came from states other than Hesse) and even among the British redcoated troops diversity could be found, with many Irish, Germans, and Scots enlisted alongside their English counterparts. Don Hagist's "British soldiers, American war" and "Fit for service" are good resources on the makeup of the crown forces in north America.

That said, it should also be noted that the war had been going on over a year before the declaration of independence was signed. Initially many colonists felt they were fighting for their rights as British citizens, but that changed as the conflict progressed (again, check out "A Revolutionary People at War" for more)