A 55 is a good size for starters and it allows you to get some larger fish. Smaller tanks can be done you just need to stay on top of maintenance.. Testing water, water changes, water top offs, not over stocking. Larger tanks are more forgiving to mistakes because of the larger water volume.
Not toping off in a small tank can lead to slainity/SG
swings which can harm fish and corals.
Money is a big factor in which way you go.... SW
is not a cheap hobby and to set a tank up right can cost some big$$$.
Do your homework and you will be fine if you take things slow..