There wasn't much expansionist zeal within Britain in 1914, the world had been divided by this period and the colonies possessed by Germany were not that appealing to Britain. Furthermore it wasn't that long since Britain had fought the controversial and bloody Second Boer War. With Germany rising in mainland Europe and Japan and America rising elsewhere, the Irish Home Rule question threatening civil war within the British Isles and the suffragettes causing all kinds of trouble, British attentions had turned away from the developing world. Financially the nation was also strained as it was spending huge amounts on the naval race with Germany, the idea of any further colonies wasn't too appealing to the exchequer.

The main colonial issues were the beginning rumblings of the Indian independence movement and the future of the Dominions. In regards to the Dominions there were some minor movements about bringing them together into a British Federation but this never gained critical weight, then WW1 intervened and pushed the Dominions towards a slow move toward full independence rather than closer links with Britain.

So why did Britain and her Dominions annex various German colonies and parts of the Middle East after WW1? Well it comes down to simply needed some material benefits from the war, the nation had to gain something from fighting the war other than just defending France and Belgium. In Germany's case it was also a further punishment and in the case of Turkey those lands had already been lost and the British just took them as opportunism, it's important to note that their oil richness was only just becoming a factor at this point, the Royal Navy had just began the process of switching it's ships from coal to oil and what would later become BP was only founded in 1908. In the case of places like Papua New Guinea and Namibia, which actually went to British Dominions (colonies owning colonies who'd have thought it?) those nations were less tired and financially stretched than the British so they viewed the acquisition of colonies more with the mindset of the Scramble for Africa than Britain's post WW1 mindset.

I do not believe so. Africa had been divided up in the later part of the 19th century and China had been forced into an open door policy with low tariffs (opium wars and Boxer rebellion). However WW1 did allow England and France to split up what had been the Ottoman empire. They divided it up through treaties such as Sykes-Pico which split portions of the middle east into areas of direct control and influence. The families which had supported the Brits were put in charge further increasing influence. Strengthened British power in the middle east also helped solidify their control over APOC.