Angels are nice in pairs and a pair might be the nicest thing, even for a big 55 gallon. A 55 US gallon tank, from our nice conservative rough guideline, would call for about 45 or 50 inches of fully mature fish body. In other words you need to look up the writeups for each individual type of fish you want and determine what size people think it will average when its fully grown and then add them all up. Once you get to be a very experienced aquarist with a lot of expensive filters, you may decide you want to push this rule some and have more fish but for most normal people its much, much better to be guided by it. Coming in with even somewhat less fish than the guideline is even better as it give you more leeway during power outages and other unexpected things.
~~waterdrop~~