Just remember while you're making your list that lighting is only part of the equation--FLOW is super important, depending on the type of coral you want, and nutrient levels matter a lot. What I mean is that if you want a soft coral tank, SPS isn't going to like it, and vise versa.
My advice would be to look at as many tanks as you can, go to lots of LFS, browse coral dealers online, just look at as much stuff as you can, before you decide the route you want to take your tank. That would be lighting part. So look into the protein skimming first.
Before fish and lighting, I would definitely get that skimmer, then start adding fish slowly while you decide on what kind of lighting you want.
I say this to everyone with a 55g... so here ya go. A few months into this hobby you're going to be kicking yourself for setting up a 55g. The tank is only 12" wide, so there is no depth. It will be tough to aquascape your tank in a way that looks great, and doesn't press everything up to the glass. If it were my tank I would seriously look into selling the 55g, and getting a 75g, as the tank is not only larger, looks WAY bigger, but will only be an additional 30 or 40 bucks.
Everything you buy for the 55g, will be the same thing you'll buy for the 75g, so the cost is really not a factor. That's just my opinion...
Are you sumping this tank, or what are your plans on the design of this? Sorry, But installations are what I do, so I'm always curious :P