I bought an enlarger a few years ago but never got around to building a darkroom, so I got rid of it. I had a Bessler 23C which is also a 6x7 enlarger, and looked to be very popular so replacement parts and accessories would probably be available for a long time (used, most likely).

I'm not sure about the bulb but that's definitely something to check out. There are specialty "lamp" (what us lighting geeks call light bulbs) distributors around which you'll probably find on the internet. You might start with Googling "projection lamps" and the part number. A lot of times it's a three letter code like EXN (this isn't it, just an example).

From what I remember, usually you'll want to use the focal length of lens that's considered normal for that format (like 50mm for 35mm film, 80mm for 6x6, etc). You'll need the lens and also the proper negative carrier to hold the film.

Good enlargers are so inexpensive these days that the biggest concern is probably the shipping cost, hassle of moving it and setting up that's what you will want to consider. I haven't kept up with the market for enlargers, but with prices at what they are there's no reason not to go top of the line.