I've always wanted to own a couple of angelfish but naturally I like the research the species first so I can make the babies happy

So I had a few questions...
1) Will 30 gallons be okay for a pair, or is that only enough space for one?
2) I hear they like taller tanks - is one of the tall hexagonal shaped tanks I see around pet stores a good idea for them? If so that's a good thing anyways because it means less room to take up, heh.
3) Still based on the 30 gallon idea, what kind of bottom feeders could I keep with them (and how many can be comfortable with the size + angel(s))? I already have some albino cory cats in another tank so I was wondering what others would behave with the angelfish. Other than that I don't plan on having much else in the tank (aside from plenty of plants and hiding spots of course), since angels don't seem to need a lot of company to be happy.
4) What are some "treat" foods the angels might like other than flakes to help vary up their diet?
Thanks in advance!