One thing that isn't a bad idea, is replacing the cables, they're 30 yrs old, that's an old cable.... I've gone through 3 used speedometer cables last year, 1st year I had the bike, and she was down for 4 days waiting on a clutch cable... CHECK OIL WEEKLY OR MORE, I learned that the hard way, mine never leaked a drop, so I thought it was safe, until I was on the way to work and I hear this really loud knocking sound, and see the temp gauge go through the roof, well, trying to, I shut her down before it quite redlined, and have to decide rebuild engine, or part out the engine... If you need parts, look on the for sale buying thread here, if you need it, we've got 5 people looking to sell it. Some things I'd go new, most things you can't. If you have an issue and don't know what's causing it, 20 people here have had the issue and know what it is. If you can turn a wrench, you can fix about anything on this bike.
The carbs need to be cleaned, she'll run now, but not that well. If you have much common sense, and can follow pictures with instructions, and have a clean workspace, you can clean our carbs with the help of Larry's carb book, he's our local carb guru...
As far as maintenance, yearly flush the radiator, check oil, add if low, change every 3k miles, and ride her until your heart's content... Also every couple years or something like that change the final drive oil.
If you don't have the manual, download it free in the general discussion quick reference, it tells you what to do at what mileage.
These are quite similar to cars, but a million times funner, and easier to work on. Need to drop the motor? Grab a regular jack, and take 3-4 hours, a bit longer if it's your 1st time doing much of it, I learned to strip a CX in about 4 hours total, with the help of my impact driver.
Hopefully you rider her and fall in love like my 1st ride on my CX, was disappointed that she was only a 500 when the guy offered me 2 for $800, but I wanted a bike bad, and that was my price range, so I bought her, put fresh gas in, used a bit of starting fluid, and off we went! So basically, I hope you find a good buy, take it, and fall in love like so many have. They get a lot of responses, from how did you build that motor, to what the hell is that, to I had one of those, I miss her, and a buddy of mine had one, he loved that bike...
Hopefully this super long post had some info that helped you, if not, it helped me remember I have ADD really bad lol