Why would German-US relations worsen because of Germany holding on to its colonies and wanting to divide up the cake among the other European colonial powers? I understand where you're coming from, but the whole prospect of the conference excluding the US AFTER they provided substantial material and personal aid to the Europeans just seems like forcing into existence former conflict in order to "spice up" your timeline (no offende intended, mind you

). An inconlusive conference or even a broken-off conference because of irreconcilable differences concerning colonialism might be a better solution. Apart from Wilhelm II's somewhat heavy-handed reign, I cannot for the life of me imagine German officials, including the guy at the top being THAT dumb, otherwise they wouldn't have come that far in the first place. They proved not to be too dumb in your timeline.
OTL Great Britain, France, Belgium and others also held on to their colonies, staying allied with the US with no overt ill side-effects. The colonial question solved itself in the 60s and 70s, although much of the groundwork was laid by the fundamental bipolarity of OTL's world - Soviet-sponsored independence movements as well as the general idea of self-determination.
With a strong, pseudo-communist USSR (the USSR never was communist or socialist in the fost place, it was more of an oligarchy) out of the picture ITTL, however, and VERY strong Great Britain and Germany, I imagine a certain growing apart over time. But that would mostly happen a generation after the war. Remember, Germans, Brits, Ottomans and Americans fought and bled together. This creates a special bond that also transcends into politics and policy as soon as those who actually were in blood, guts and mud up to their necks together cease being soldiers and become decision makers in their respective societies.
So, to sum up my ramblings, I concur with the eventual outcome in German-US or rather, European-US relations, but not with the way there. Being a serviceman myself, I may be a tad too romantic in my view of a feeling of brotherhood among soldiers from different countries, but my experiences tend to support that kind of view.
Speaking of which...I wonder how Europen-Russian relations will look like after hostilities cease. Will Germany and the other combatants be magnanimous in their victory or are you planning on small-minded, petty and harsh conditions? I hope you butterfly into existence a far-seeing and wise decision by the victorious countries, otherwise the stage is set for decades more of low-intensity warfare and terrorism...