Nice pick up!
Welcome to ThePlantedTank!
For a 75 gallon at 48 inches, a Satellite Freshwater LED+ fixture size at 48 inches and is extendable to 48in-60in would work really well for your tank, IMO. One of the best options about this LED+ is that you can adjust the lighting, because sometimes you can end up with too much light from T5's, PC, etc, but with this led fixture, you can fixture accordingly to what works so you can avoid algae issues. You can also change the color, have night lights, with a touch of a button on the wireless controler etc. Pretty awesome customizable settings. There are presets too. Low tech is definitely a great choice, if you don't want to deal with pruning/trimming plants frequently, deal with co2 equipment and buying/making co2, dosing a lot of ferts, buying lights and getting the right intensity level, testing, water changes and all that; I mean, unless you have a lot of time on your hands, then it'd probably be fine.. but if you're a busy person with a lot going on, work, school, social life, etc.. believe me, it's going to be challenge at times to keep up with maintenance and it doesn't become fun anymore, in my opinion. However, if you keep a rather small high-tech tank, then it's a different story, things will be a bit easier, but on a big tank, it's quite a bit of work.. Ah it really comes down to you and your decision. Not here to say "GO LOW-TECH!" And hate on high-tech. There are pros and cons to both.
Check out this thread of low light, low tech plants if you are going low-tech. It's a great compilation of plants that can do well with low-tech tanks.