I think a 2 bulb Catalina T5HO light will be too much light for a standard 55 gallon tank, unless you are willing to devote large amounts of time to maintaining the tank, and adjusting the CO2 system. A one bulb light should give you low medium light, which lets you grow just about any plants, with CO2, although the red and orange colors in some plants may not be as prominent as you expect.
"Enough" light is really dependant on the type of plants that you intend to keep. Anubias, stems, etc. would be fine with that light. More light intensive species, red plants, etc. will require more light. There is a sticky at the top of this forum with par data collected by Hoppy that is very informative. I would advise you to start there and make your selection based on what you intend to keep.
Also bear in mind that it may be wiser to go with a fixture that puts out more light than you like. You can raise this light above your tank to compensate for the difference. Then, should you choose to alter your plans down the road you can simply lower the light and save yourself the money and hassle of having to buy another light fixture.