I got a Kowa 66 with three lenses (55, 85 and 150) very cheap and it's my favourite camera. It's quirky and unusual, but I love it. A Super 66 would have been better, but they're usually a lot more expensive. It's probably the heaviest 6x6 SLR you can get with all the advantages and disadvantages that brings. Carrying it all day is hard on your back, but the weight allows for relatively long shutter speeds without a tripod. I also find the mirror slap pretty soft, though I can only compare it to a Kiev 88CM I once had, which caused light earthquakes with every exposure.
So, for your questions:
1. The one I got is very well made. There was some damage to the leather, but the inner workings are as new. I specifically bought one that looked a little beat up, because that's usually a sign for a camera that did good work for decades and will do so for another few. The ones that look new, were probably not used, because they've got a problem. From what I've read, the factory had pretty good quality control.
2. Built like a tank. Not Leica quality, but good enough. The ones that weren't as reliable, are probably completely broken by now. I never had a problem with mine.
3. There are very few people who know how to repair one and not that much information on the internet either. But as the shutter's in the lens, there's actually very little to break in the camera itself. If you have some experience with other mechanical cameras of that time, you'll work this one out, too.
4. I love the lenses. They're not Zeiss quality when you look at resolution and sharpness, but they all have a very nice "style". You know, when a lens is not technically the best, but has great bokeh and that certain pleasant softness instead of just being unsharp. At f/8 they can be very sharp too. I have seen very few (and usually much more expensive) lenses that were better for portraits. I regularly make 50x50cm (20x20") prints and they look great.
5. Very easy to use. You have all the controls right on the lens (including flash sync and self timer) and nothing else. Ergonomics are always about preference, but I like it the way it is. It just fits into my hands. I have a bassist's hands, though, so that might be a problem, if yours are relatively small. The only thing I don't like, is the shutter safety. It's a little knurled ring around the shutter button that's somewhat hard to reach and (at least with my camera) hard to turn. If you don't use it, the shutter goes off very easily and sometimes accidentally.
If you can get one cheap, go for it. They're great fun. You definitely want to take a look at the Bronica SQ, too. I never had one myself, but from all I heard, it's a great camera and pretty cheap at the moment. Just don't go for the Kievs, those crappy soviet copies of Hasselblad cameras... for the price of the CLA and necessary repairs, you can almost get the original HaBla500. The upgraded Kievs from Arax are supposed to be ok, but then again, for that price, you can get a Bronica or Kowa with a few additional lenses.
