First off, welcome. I also had an XS750 before this bike, a '79 Standard full dresser. I really like me that triple. I've had a '99 Conc for almost ten years, and 130k miles of it's 159k.
Mods. In general. Do some reading in the forums, here and the "Ofishall" COG one, on what folks have done. Get to a gathering, RTE, rally, tech session, whatever. You'll be able to talk to other folks about what they have done and the results. You did not disclose your location for help in this regard, top secret?
Lighting in particular. Do NOT go to a higher wattage bulb without installing a bakelight headlight socket, at least. Also very helpful to install a headlight bypass wiring setup, using upgraded wire vs the thin stuff MaKaw uses. It alone will make a significant difference in light output and will remove a heavy load from the J-box. A good thing. Some folks have gone the HID route, I did, and went back. My FF200 lights completely drowned out the HID. I did not like the added complexity, and it quit working after about 2-3 months. An HID failure with no added lighting will leave you "in the dark"