Angels are hit or miss, but some are worse then others. IME, a bi-color is the worst reef safe dwarf angel (( with a lemonpeel a close second ). Plus, they have poor survival rates.
Over the years I have had 3 flames, never had any of them nip (( I mainly keep SPS )).
As for the snails, I would start off with 5 or so, and see how they are doing. Better to buy more later, as opposed to getting too many now and having them starve.
In my 29 I have 2 -- one trochus, and one Mexican turbo. Also have two nass snails.