The 55 gal
. aquarium is probably one of the most popular tank sizes. There is a lot of very nice things you could do. I would start off with a good deep sand bed, seeded with about a gallon of substrate from a good dealers tanks. Add about 40 # of Dry Rock, (cheaper) and maybe 10# of live coraline covered live rock (i like fiji) toss in a few reef hermits, maybe a brittle star, and let it cycle. While you wait for that to settle in > read, read, and read some more. There are almost an endless number of fish and inverts you could house in a 55. I lean toward low stocking. But to each his own.