OK, keep in mind I am trying to help you do this without trashing all of what you have. You can certainly re-use or re-purpose your equipment that you have now. That's part of the fun of it, coming up with ways you can do this within your budget and to best attain the results that you want.
I know it is overwhelming to try to figure all this out. It was for me just recently when I got back into the hobby. Just keep in mind this is a fantastic opportunity to create your own beautiful world. Is there a tank here in the tank journal section that inspires you, maybe catches your eye? Something you would like to emulate? Link it so we know what direction you would like to go. Do you have a budget in mind to get all this done? That helps us put a frame of reference so we can recommend things that would work best all the while keeping you in your comfort zone.
People are gonna recommend that you go and purchase all new stuff because what you have is "wrong" in their opinion. You CAN use an UG filter with a planted tank, in fact I am doing it right now if you you would like to look at my journal (I need to update it). I also had a very successful planted 55g years ago with the same type of filter setup that I use now. Here is how I set mine up:
I mixed flourite "red" substrate with my regular (medium sized) aquarium gravel, about 60% gravel and 40% flourite. You could also use Eco-Complete instead of flourite. I used "natural" colored gravel to better blend in. When you look at gravel at your local fish store (LFS as it is called here) you will notice there are many different sizes. Think about your UG filter and get something that will in no way impede or fall through it. Honestly that gravel you have is...well...ugly. Plain gravel is cheap so I would recommend getting something that looks more natural to your eye and mix it. This will help you save money and provide a nice substrate for your plants to root in and they will draw some of the nutrients from the flourite/eco-complete and fish waste/plant matter and help them grow. I then "capped" in another words, put a top layer of the fine substrate (eco-complete) on top of the mixed gravel/flourite. It has been working very well.
If you look at my setup, you will see I connected where the updraft tubes are supposed to be on the UG filter to the intakes of my hang-on-back filters (referred to as HOB here). This allows the flow of water through your UG filter over the bed of beneficial bacteria that will form there and into your hang on back filters where you can add your choice of: carbon to clean/polish the water, BioBalls to foster even more beneficial bacteria, or other filter medium. There are many. Some like Seachem Purigen that does the same job as carbon, only better and can be "recharged". You could add bags of Cuprisorb which removes copper to ensure the health of your livestock, etc. The choices are endless.
I have two HOB filters drawing from my UG filter full time, another comes on only at night with an airstone to help the plants/livestock get their oxygen at night. During the day plants use CO2 and nutrients and make O2 and grow. At night, plants use O2 to sustain them until the next light cycle. This is why it is important in my mind to run an airstone at night. Some people prefer to do it all day, I don't. That's the beauty of it, as long as what you are doing is working, and making you, your fish and plants healthy and happy then go for it.
Whew that was a long write up for me. Anyway, next onto lighting. I will ask a question to get it started, what is your budget? If you are not going to go pressurized CO2, I would stay far away from the "high light"(high par) fixtures. You would want to stick to medium light. Way back when, on my 55g I had two double light fixtures running (4) 40 watt lights as a reference. I didn't use CO2 back then just liquid fertilizers as I do now and it worked very well.