If Woodrow Wilson was not President in 1914, would the United States come into WW1/The Great War earlier or latter?
And would the United States actually join the League of Nations, or would this sort of TL lead to a Central Powers victory?
It wouldn't matter actually too much. Wilson was a pacifist, so he actually might have delayed America's entry into the war. Though, I can't say for sure as America wasn't willing to commit too much in Europe after seeing the bloodbath in the Western Front.
Nope. America would still stay isolationist and, in fact, there might be a good chance the LoN won't even be made if Wilson wasn't president. It was his idea and the 14 Points that basically introduced the idea of a world organization and the such.
And there was no way the Central Powers could ever achieve victory in WW1 unless the invasion of Belgium was swifter and/or the French army mutinied/defeated in the opening days of the war (which is very unlikely). By 1915, it was pretty much clear that the Central Powers lost. America's entry did shift the balance, but even if America just financed and supplied France and Britain, it would only delay the inevitable as the blockade on Germany would force them to crumble from shortages.