I would start with 8 smaller angels, with the understanding that you will be returning some when a pair forms. Most independent shops are cool with this, and have no problem taking back larger angels, as they are generally good sellers.
You now have a pair, and can continue stocking around that. If you want to try for a species tank it's a little more tricky. If my math is correct that tank is around 65 US gallons. You could keep 6-7 adults, only issue is compatability. Some pairs are less aggressive, taking a small area for their territory, others will claim the whole tank.
I was able to keep two pairs plus 3 unpaired fish in a 65 gallon after switching some pairs, it took a few tries. Decorations also come into play, the more decorations you can add to act as a natural divider the better, as angels key territory off of objects in the tank. You want to break up the line of sight as much as possible with multiple pairs, if they can't see it it's not a threat.
If you want to go by gallons per fish, a breeding pair needs 20 gallons minimum, each breeder size angel needs 10 gallons. Potential breeders need 5 gallons of space each. This takes into account water space needed, not territory, each fish is an individual as far as territory needed.
For the sake of safety keep a divider handy, as the fish grow there may be some aggression issues, and you want to keep any damage to a minimum before you get a chance to return any fish.