Hey - good questions!
As you've seen, different players have different angles for rasgueados. Mine's a little more 45 degrees than perpendicular, but sometimes I'll go more perpendicular for a specific sound. In general, though, you want a default angle that's comfortable and sounds good. Until it's relaxed and comfortable, I'd prioritize that over sound. So find the position that feels best and get as relaxed as you can. If you're actually missing the strings with any of the fingers I'd suggest you adjust (that's kind of a deal breaker as it messes with your rhythms), but other than that a relaxed rasgueado is the most important thing. Once it really works at whatever angle you choose, you'll find that making small adjustments when you want a different sound won't be as big a deal.
As for the rasgueado and alzapua and how many strings to hit - that's one reason I hate notating either. For rasgueados I find in some instances not all fingers are even hitting exactly the same strings, but the totality of the rasgueado gives the chord the way I want. Again - missing completely with one or more fingers is a problem, but short of that I'd go for relaxed hands and even time before worrying about exactly which strings to hit or if the upstroke is identical to the down. Kind of the same for Alzapua. Generally you don't need to hit more than two strings of the chord, especially if you're going fast. Sometimes you'll hit an open string and it just sounds plain wrong, so in that case you know to avoid those (same with rasgueado). And don't worry if you hit different strings on the way down than on the way up - this sort of happens naturally until your alzapua gets really under control. As long as it sounds like the chord you want and you're happy with the sound, you're good.
And really that's the bottom line with all of this - if it sounds good, it is good (as long as you're also relaxed so you can keep doing it a lot!).