Hello and welcome to the fishkeeping hobby! It's quite an addicting one that I'm sure you'll grow to love. A 55 gallon is an excellent size tank to start out with! It depends what type of fish you're specifically looking for when it comes to stocking
Many varieties of small schooling fish- neons, other tetras, guppies, etc
Or a few species of larger fish- angelfish, gouramis, small cichlids etc
Some fun fish to have would be a pair of angels, a gourami (as they're super colorful and personable little creatures), Cory cats, German blue rams, and any larger non-nippy species of tetra. You could also create a dwarf cichlid tank as there are many peaceful and compatible species of dwarf cichlids which are beautiful and interesting little fish to observe. A light isn't 100% necessary unless you plan to have a planted tank (which I highly recommend). If you choose to do a planted tank, which has many benefits including a natural environment and keeping good water quality, then a powerful high quality bulb will be needed according to the species of plant which you plan to keep. A good lid that includes a light fixture can be bought at just about any pet store and will fit most standard tanks, so that can easily be sorted out. As for filters, I always recommend choosing a filter that is made for a tank 10-20 gallons larger than the one you have. So if you had a 50 gallon tank, you'd go for a 60-70 gallon filter. Something important to get when starting up is a water testing kit. These are essential to keep your tank running properly. I recommend the API master test kit. Another important piece of equipment would be a heater. This is an essential component in a tropical fish tank to maintain healthy and happy fish. I hope this helped, enjoy setting up your tank, and if you have any more questions, ask away!