Ukrainian or Russian
I set my mind on learning Russian a long time ago, so since it hasn't come out yet, I'm debating on continuing with Ukrainian. The reason is, ukrainian letters and words aren't completely different, but I'm afraid that I'll mess up my Russian vocabulary by learning Ukrainian. What do I do?.
If you want the learn just basics like the alphabet it shouldn't be any problem. Even if you go further you can learn some basic grammar (cases) which is the same in Russian just to understand what they mean, but you should keep in mind that the endings are different. Honestly the Ukrainian course isn't the best one here on Duolingo, there are too many mistakes in it so I hope they'll keep working on it.
Agree. Letters are almost the same and cases are similar (the main thing is the concept in my opinion) ... There will be some differences in words spellings and some of the words are totally different from russian, but I think it won't hurt at least to start it. As Michal_90 said there are some errors in Ukrainian course... but they are being constantly worked on, so it is getting better.
Maybe try memrise? I am sure they have plenty of Russian to tied you over until the Duo course arrives.
If you want to learn Russian better not to start studying Ukrainian. Then there will be confusion. I mean deep language learning. If this is a cursory examination you can safely learn Ukrainian! I learn English, so I apologize for any possible errors :)