Have to say well done!
Never had Amanos, are they OK in soft(low PH water) that is what we have in NYC.
Are they OK to keep with large Angels?
Well, the rule for shrimp and fish is, if it can fit in their mouth, they'll eat it. That being said, in a heavily planted tank with plenty of deep foliage and hiding spots, if you put the Amanos in first, they might be ok. But truthfully, I would expect their number to dwindle over time.
What about using antibiotics? I've heard this mentioned before but I'm not aware of the specifics.
Erythromycin is the antibiotic of which you speak. It's used to combact "Blue Green Algae" which isn't an algae at all, but a cyanobacteria. It's typically caused a combination of factors including low nitrate and low water circulation.