Actually, you really DO need a protein skimmer for any tanks over 40Gallons. So for a 55, i would definitely recommend one. That's a lot of water, and just having a simple HOB
or canister filter running on the tank won't do much for filtration. Having as much live rock as you do now, will count for a good amount of biological filtration, but you still need something to count for mechanical filtration in a tank that size. Also, Jebo skimmers don't have a very good track record from what i've heard, so upgrading your skimmer solution might be something to look in to. There are way more brands that are fairly cheap, and are a heck of a lot better than Jebo skimmers. Jebo skimmers are like SeaClones.. which are terrible skimmers and don't have a good track record either.
As for the lighting, since you say it's a 48" fixture, with 4 bulbs, my guess is that you have 216w's total.. which isn't all that bad. I'm no light expert, but judging by your fixture, and if those reflectors are well-made, then i would say you could support softies and some LPS
.. but any of the low-light SPS
you wanted to support would need to be placed near the top of the tank. The most common 55G tanks are 21 inches tall, and that's a lot of water for light to penetrate through, unless you have a differently sized 55G tank. Giving us the tank dimensions would help us to let you know what coral you could support with the fixture at hand. If you bought a fixture such as the 48" Nova Extreme Pro, which is a 6-bulb fixture, you would be able to support any coral you wanted. However, since you say you are upgrading to a larger tank in the future, maybe you will want to go with a Metal Halide solution that you would be able to bring over to the larger tank when you get it. Buying a lighting solution that can support multiple tank dimensions now, would save you money in the future because you wouldn't have to scrap or sell the old fixture to buy a new one. I'm buying a MH
pendant now for my 25G and if i ever plan on upgrading to a larger tank, i will still be able to use it since it's an excellent light, and metal halides are among the strongest lighting solutions and can penetrate deeper through water than most other lights can. Just my thoughts on the lighting matter.
I also agree that good coral to start off with are mushrooms and zoas. Those a pretty good test corals.