Several things I'd like to point out.Britain most likely not join the entente side in this scenario.What might happen is that Britain might issue an ultimatum at Russia asking it to fuck off from the Bosphorus.The Ottomans also don't have a formal alliance with Germany.At this point,it was neutral,with the navy being pro-British and the army pro-German.So I've decided (mainly in the interest of keeping thing moving smoothly) on the first phase of the war being Britain/France/Russia/Serbia/Greece vs Germany/Austria/Ottomans with Italy staying neutral for at least up until where we are now (1923).
War begins due to a Balkan Conflict between Russia and the Ottomans which leads to the Turks calling the Germans which leads to Russia calling France and in turn, Germany calls Austria to deal with the Balkans while Germany attempts to focus on the bigger powers.
By 1922, the Congolese decide to take the German's call, and begin to invade French Congo and Portuguese Cabinda while simultaneously giving troops (mainly Zanzibari) to defend German East Africa.
As of 1923, the Balance of Power in Africa has drastically swung back in the favor of the Central Powers. France, Portugal and Britain are bleeding out and losing thousands upon thousands of men and an insane amount of resources they'd otherwise have alongside having to put down small revolts within the colonies are probably being tried and suppressed (not much of an overall impact, but a nuisance). Critically, the lack of Congo's rubber and copper following its entry into the war is both huge and damaging to the Entente. Not crippling, but damaging.
I also imagine that the Middle Eastern Front has been greatly affected. The Gaza line is having a much easier time being held by the Ottomans thanks to drastically better infrastructure and communications alongside simply not being utterly exhausted from the Balkan wars. Meanwhile, Britain has to stretch more and more of her forces alongside calling greater amounts of (white) colonial troops. The Dominions are not happy.
At the same time, the Russians are stuck having to battle the more developed Austrian Empire, the motorized Germans and fight a third front in the Caucus against a better supplied Ottomans (although in turn, the Ottomans are stuck fighting in the Balkans).
I also imagine this probably means Ethiopia would declare war on the Entente given ties with Congo and opportunity to take some coastland via conquering Djibouti and British Somaliland. Yet another headache for the Entente. The Ethiopian army here would be stronger than it would historically due to veterans who served Congo, a larger army and economy because of the Congolese trade, and because of more armaments (critically artillery) from Congo.
Would be fun to see them fight against the (relatively) tiny garrisons in Djibouti, Somaliland and Egypt. Although the South Sudan front would not be pretty for anyone.
All in all, its a bigger, bloodier, more widespread and much more destructive conflict that sees the Entente have to put out many small fires alongside focusing on their main targets of Germany and Austria. Very bad news for France, who's going to be taking a battering in this war.
Re: Sudan. I do agree, having what's South Sudan be part of Uganda makes sense, even if those borders are just disgusting (Then again which border in colonial Africa isn't?) and it allows Egypt to control a much easier territory. Darfur is probably de facto independent but no one really cares about some nomads in the desert at this time.
Re: China. A messier dissolution of the Qing would lead to a whole mess of a Warlord era and all sorts of problems that Japan would be eager to exploit. Can't really say anything further. Any suggestions on what a China front in WWI would look like?
As for China and Japan,Britain and the US would be greatly displeased at the Japanese for attacking China.I don't know their exact reactions though.Britain's completely distracted by the events in Europe while the US is still relatively isolationist.Another thing to consider is that even with China being completely overrun with warlords,Japan would be immensely weaker than otl Japan in the 1920s since they wouldn't have profited from WWI.