Going to be tough to answer any of these questions with authority, as I do not bake much, and nothing I’ve ever baked has used sour cream. My experience with sour cream substitutes is just slipping it on top of tacos/fajitas/burritos. And for that purpose- it works just fine.
Regarding using four cream as a thickener for soups- any thickener is going to work. Another poster suggested coconut cream, that works well for me. Adding starch of any kind will also work to thicken soups. If you’re looking for extra protein: blend up some cooked white beans, or silken tofu works really well for this too.
Now for your question #2: I don’t know if I’ve ever encountered vegan sour cream with oat or almond bases, but I know when comparing oat/soy/almond milk— the soy is the only one with protein and fat content. Oat and almond milk tend to have very little nutrition, and are mostly cloudy water (exaggeration). So I tend to use unsweetened soy for most my cooking. Your mileage may vary.
Good luck!! And remember that you don’t have to only cook from physical cook books- the internet is LOADED with good vegan recipes. Do some experimenting. Don’t be discouraged when something doesn’t turn out, it takes a while to get the hang of using so many new ingredients!
Great news. Now if we could get other chip makers to take out milk powder from all their “salt and vinegar” chips. It’s in the goddamn name: salt, and vinegar!! Not “salt and vinegar milk”
Sorry, just had to vent about this frustration.