One thing about your water parameters.......you won't have to worry about a ph crash with your kH as high as it is.
My advice, whatever else you decide to do is to work initially on building a nutrification system and balancing your tank. You have many elements in place to have a nicely planted tank and should be able to grow many varieties of plants in it.
Tanks that are not established need time to balance and therefore are subject to algae issues. Many people are now placing a thin layer of plain peat moss over the bottom of the tank before laying in the substrate. This is sort of an 'instant aging' process that has worked well.
If you have access to a healthy established tank, take some of the filter media out of that tank and place it in your filter. This will greatly reduce the time required to build the nutrification system.
I would get as many plants, especially nutrient hogs initially, and let them get a foothold and start growing, to get the jump on the inevitable attempt by algae to rear it's head.
CO2 is a tremendous help for plants at any wattage, but becomes almost a necessity at 3.0watts/gal. and up. For a 55 gal. tank DIY CO2 is not very effective, and a lot of work. I would consider a pressurized system in your case.
If you keep asking questions, you'll find that we are very adept at spending your money
. Once you have collected the necessities however, you're pretty much home free and can get on with enjoying the hobby.