Ukrainian vs Russian
I recently started the Ukrainian course and have seen a few comments in the discussion that it's a little limited compared to others being offered here. A few people have suggested I also consider learning Russian to augment my learning and I am very willing to do it.
How different are the two languages when it comes to the vocabulary and meaning of words/phrases?
If you are not fluent in one of the languages (Russian or Ukrainian) you will mix up Russian and Ukrainian words. It happens when you learn similar languages at the same time. There are many similar words in both languages; spelling and pronunciation can be a little beit different. You can mix up these kind of words. It happens to me when I started learning Italian and Spanish. I know better Italian and when I speak Spanish, very often I use Italian words insead Spanish ones.
Knowing Russian, I understand maby 30-40% of Ukrainian words. You have to decide what language is more important for you. I advise you to learn one of these languages for 1 year and then you can start learning the 2nd one.
Although the languages are pretty similar, I'm not sure it's worth to learn Russian if you need Ukrainian (or vice versa). If you plan to speak both languages eventually, then you'll definitely find a lot of similarities between those languages. But if you only need Ukrainian, then Russian course just seems unneccessary.
Yes, the Ukrainian course is smaller and has more bugs than the Russian course. But it should be enough to give you a foundation to continue learning on your own, using other materials.
I personally think this is a bad idea. I had an experience of trying to learn both Cantonese and Mandarin at the same time, and I still can't speak either. But your mileage may vary.
Really it depends why you're learning Ukrainian. If you just want to be able to speak a Slavic language, then the Russian tree is more thorough and much more informative. However, if you really want to learn Ukrainian, then Russian could be somewhat of an unnecessary detour.
If you can articulate for yourself why you chose Ukrainian, that should help in figuring out whether you should stick to it or go for Russian first. If you have Ukrainian speaking friends/family, then you have an obvious reason to prioritise Ukrainian.