Right on! Sounds like we have similar tanks!
Angels and gouramis will be fine, just watch for fin nipping - as angels have huge fins and gouramis are notorious for it. (Not saying it will
happen, just something to watch for)
Rams are a good match too, bolivian are supposedly a little more hardy than the GBR - so if you're new to freshwater like I am, maybe consider those! I'd say maybe 2-3?
Apisto cichlids (like cockatoos) are fairly hardy and can be non-aggressive, as they are small and in a huge tank. I wouldn't do more than a couple though, as they'll get territorial - keep this in mind if you do rams, because the rams and apistos may fight for territory as they age.
I also have a school of 10 X-Ray Tetras in my tank, I think they're cool looking and I wanted a small school. It's awesome to watch them go nuts at feeding time! I trained them to eat out of my hand, so whenever I put my hand in the tank they all rush it and go nuts
If you go cichlid, stick to either North/South American or African. Don't mix and match. I've also heard keeping them around the same size is a good bet. They may (likely) attack the gouramis though. cichlids can be little buttholes about their territory and will go after anyone that gets in the way.
Just some suggestions. If you like angels, go for it. They're beautiful fish and can get a good size once fully grown!
I think 3-4 is the max on angels for a 55 gal
(again, I'm fairly new, so anyone more knowledgeable please correct me if I'm wrong)