Poor guy. Since he's older and not in the best shape, I suggest offering drops of water on his nose to help
hydrate him. If he takes water, keep offering small batches several times per day for the first day or two. Offer him a salad and see if he will dig into that. If not, you may want to try dripping some baby food squash or green beans on his nose and see if he'll take that. Most of his diet should be veges so I suggest 2-3 items from this list each day in a salad for his main diet
http://www.beautifuldragons.com/Nutrition.html. A variety of bugs is good too. Dubia roaches, crickets, silk worms, horn worms, and black soldier fly larvae are all good to offer on a rotating basis. He should only have a bug meal every 2-3 days though, especially if he's eating plenty of veges. Hold off on the bugs for a little while though because the protein may harm his system if he's flooded with it all at once.
As far as tank size goes, I suggest at least a 40g breeder tank (this is better than a 55g tank). Pick up a dome fixture for the basking light and a PAR38 halogen flood light. A 75w (not energy efficient) should do the trick. I would also get an inline lamp dimmer or a dimming thermostat so you can adjust the output. An adjustable lamp stand will let you raise/lower the lamp to adjust temps too. I would pick up either an IR temp gun or two digital thermometers w/probes like this
https://www.amazon.com/dp/B0017N8W90/ so you can monitor the surface temp in the basking spot and on the cool side of the tank. Shoot for 100-105 in the basking spot and about 75-85 on the cool side.
I suggest getting a nice 22'' T5 UVB tube and fixture for UVB output. Investing in high quality UVB is important. They may not carry it in a local store so it may need to be ordered online. This is a good combination to look for
https://www.amazon.com/Zoo-Med-26061-Reptisun-Fluorescent/dp/B00AQU8HAO and this fixture
https://www.amazon.com/Sunblaster-904296-NanoTech-Fixture-Reflector/dp/B00AKKUBDQ/
Go with a solid substrate for the tank. Ceramic tile or non adhesive shelf liner are good options because they're easy to clean and sanitize. Avoid loose substrate like sand because it's tough to keep clean and sanitary.
That should cover most of the basics. If you have specific questions please let us know. If you'd like to share photos of him, you can upload them here
https://www.beardeddragon.org/useruploads/ and post them to your thread using the XIMG button.