Welcome to the forum!
If it runs at all you're doing pretty well. Not idling is probably caused by blocked passages/jets in the carbs.
Does it have stock air intake filters and exhaust?
If yes I wouldn't worry about a carb rebuild kit. Maybe just gaskets and a good cleaning or two, or three, should suffice.
If it does not have stock intake & exhaust the carbs might need different jets to fix the idle issue.
Don't buy a rebuild kit. Many rebuild kits don't use genuine Mikuni jets and don't come with the correct jet sizes anyways. There are stores that sell genuine Mikuni jets and parts.
Shouldn't need to replace the carbs entirely.
Inspect the rubber bits:
The boots between carbs and engine tend to dry out and crack.
Check the tires. You'll probably want new ones pretty quick either way.
Check the brake cables and lines. You're really just checking for function. If they work, great.
I think that model should have an indicator for rear drum brake wear. There's a little arrow on the rear drum that rotates as the brake is pressed. If it rotates all the way down-scale you'll need new brake pads.
Check the front brake caliper pads visually.
If any rubber needs replacement maybe the seller can be haggled down in price.
If at all convenient check/ask if the oil filter cover can be removed. Over-torqued covers get stuck and have caused members big headaches.
More of an issue on earlier models as later ones actually had the torque spec cast right into the cover.
If you do check it, don't actually take the cover off as it will drain oil everywhere. If the bolt moves at all you're good.
It runs so compression is probably decent but if you have access to a compression tester you could check that too. The procedure isn't complicated and has been documented a few times on the forum.
Keep in mind, you are buying an older bike. It will need more maintenance than a brand new machine. Get it running well and do your oil changes and it should be happy though.
Good luck!
