Another Saltwater Newbie!

Hey all, I'm new to the forum and new to saltwater, and I've been thinking about turning a 55 gallon tank (that currently just houses a lot of dust) into a saltwater aquarium. I plan to start FOWLR, but maybe add some soft coral (mushrooms and zoos) and possibly a couple of the hardier stony coral (bubble coral, maybe? I love its look) after the tank is established in a few months. Here are my big questions:

The biggest is that I live in a house that I rent and I know I will be moving in 1.5 to 2 years. Where, I'm not sure. Very likely out of the state. Is starting a saltwater tank, when I know I'll have to break it down in a couple years, the very definition of madness? Am I wrong to think I could move fish, coral, LS, LR etc, etc and set it up again on the other end with minimal disaster?

I've been reading a lot about deep sand beds. When are deep sand beds ideal? What depth of sand should I be planning for if I just want a, well, an average depth sand bed? ;)

I want to have a great setup, but I also want to have (as we all do) an affordable one. I know I need a filter, a heater, some powerheads and a protein skimmer. Is this right? What are the 'essential, must-have' pieces of equipment and what are the 'these can help, but aren't necessary' pieces of equipment? I plan to start with the lights I currently have (my old freshwater tank was planted, so they're 'daylight' tube lights', but I know I'll have to upgrade to actinic/T5 lights when I'm ready to add coral. Or, is it better to get the lighting now to promote happy liverock? I also want to get a Mandarin Dragonet down the line, so I want to make sure my setup allows for lots of copepod growth. If I want a Mandarin, do I need a refugium?

This is my current fish list (probably in the order I would add them):

6 Blue-Green Chromis
1 Chalk Bass
1 Purple Firefish
1 Royal Gramma Basslet
1 Mandarin Dragonet (after 6+ months)
1 Coral Beauty Dwarf Angelfish (maaaaybe, if it won't massacre coral and beat up all the nice, shy, passive fish)

I was also considering a six-lined wrasse, though it sounds like they can be a bit aggressive, and I'm trying to stick with passive live-and-let-live folk. How does the fish list look? Any obvious problems? Is this too many fish for a 55 gallon tank?

What other words of wisdom can you share? What's the one (or two, or three) things I should know that you wish you knew when you first started with saltwater tanks?

Teach me! Mold me! Don't let me inadvertently kill everything! ;)

Thanks so much, everybody!

--Kacey