Bioloads (and a few other wee questions)???

Well for one thing, you don't want to put only two angel fish together unless they are a mated pair. I'd say only go with one for a 27 gal.

Also I would not recommend you putting a betta and an angel fish in the same tank. I've read they don't get along.

But I don't have any experience with that.

I agree about the betta, some will get along, most won't.
The rams are supposed to be pretty laid back, tho.

Maybe a dwarf gourmai? They are very colorful and if you keep only one they are pretty peacefull (also very colorful, especially the red ones).

The list you have above would be a heavy bioload of not entirely compatible fish and, IMHO, you'd be overstocked.

That cm per 2l formula is the metric version of an inch per gallon. It's not a great rule of thumb. Even by that rule, you're listing about 37 inches of fish.

Mass increases exponentially as length increases. If you look at one of the tetras and then you look at one of the angels you'd figure the angel is about twice as long the tetra… but its a lot more than twice as massive, requires more than twice as much O2, produces more than twice as much waste.

An inch per gallon (or an inch per 12 square inches of surface) isn't a bad place to start, but you need to allow for variables. Bigger fish count as extra, speedy fish count extra, carnivores (with protein rich diets) count extra, and heavy bodied fish count extra.

I don't know what shape your 27g is but you'd want a decent height for the angels.

You've also got three different centerpiece fish, each of which can be territorially aggressive. Too crowded.

You'd be better off with one (type of) centerpiece, a school, and group of bottom-dwellers. Personally I'd go with the Rams, double the tetras, add a small group of cories. Lose the angels and the betta.

PS (edit): crowded stressed out fish don't behave well or display well. You'll get more interesting behavior out of more colorful fish if you design the stock in a well-balanced and moderate way.