As an answer to the OP,
yes an independent Ukraine is possible but its not going to be easy. Firstly, sooner rather then later the Ukraine is going to end up under Red Army control, assuming of course that the Russian Civil War goes similar if not the same as IOTL. Wrangel in the Crimea won't be able to oust the Reds and, once he's defeated as IOTL, the whole of the Ukraine will be under the control of the Bolsheviks.
Otherwise, you could explain the existence of an "independent" Ukraine by having Germany win WWI and consequently go on to rule Poland, the Ukraine, etc. as eastern client states.
Or, you could have Poland win an overwhelming (and unlikely) victory in the Soviet-Polish War and go on to unite Belorussia and Ukraine into a federal union under Polish control. The Ukraine still wouldn't be entirely independent in this scenario, and IMHO is similar to the situation that the Ukraine in real life post-civil war faced (i.e. the Ukraine existing as a federal state in a much larger union of multiple nations)
All of that being said, its hard to create a scenario wherein the Ukraine gains full independence.
If we butterfly away the October Revolution (and thus the Russian Civil War), we might be able to achieve an independent Ukraine as Ukrainian nationalism and talk of separation from Russia proper was already taking place under the ineffectual Provisional Government. But then we still have a situation where the Germans inevitably move on to occupy the Ukraine during their counteroffensive on the Eastern Front, which means that we'd almost have to butterfly away WWI as well to achieve true Ukrainian independence. Even then, if we ruled out the Great War as a factor, the butterflies would be such that the Ukraine still wouldn't necessarily gain independence especially assuming that the Russian Empire stays intact in the absence of WWI.
My point is that its really hard to simply
make the Ukraine (or any of the Russian minority nationalities for that matter) truly independent as the situation both in real life and in your AH scenario is unfortunately very complex.
I'd suggest that you keep working on your mod, take other people's suggestions, and try to come up with a plausible way for the Ukraine to achieve at the very least semi-independence if not full independence. Do your homework too, as research can go a long way in creating a decent alternate history scenario.
I look forward to playing your mod, and already I think that it is interesting. Keep working at it, and try to carefully build up your AH timeline in the same vein as a fantasy world - a good alternate history is well thought-out, thoroughly researched, and imaginative.
I myself might make a mod, based off of a defunct timeline of mine.