There is only one small caveat in my mind: if this is the Koni Omega Rapid, it is the first model of the Koni Omegas, and it takes different backs from the later Koni Omegas and Rapid Omegas. It is harder to find the backs for the Koni Omega Rapid on eBay. But, if the camera is working and the two backs are enough for you, maybe you don't need any more backs.
As with any older camera, depending on how it has been maintained, the light seals might need to be replaced and the backs might need to be serviced. The Koni Omega service guru is Greg Weber, and his web page is at
http://www.webercamera.com/
The 90mm lens is a Tessar formula lens and very sharp, particularly when stopped down. The other lenses are the 58mm, which is sometimes marked 60mm and takes a separate viewfinder which goes in the center accessory shoe, the 135mm and the 180mm. These are very reasonably priced on eBay, with the possible exception of the 135mm, which is more rare (depends on what you call reasonable). All the lenses are good and have been favorably compared to much more expensive lenses.
The camera itself was made for professional use and is very rugged. There isn't much to go wrong, unless the rangefinder needs to be realigned.
As I recall, the Koni Omega Rapid was made before the 135mm lens was produced, and therefore there is no marking in the viewfinder to indicate what you are getting with that lens, and the distance scale on the focusing knob doesn't include the distances for that lens.
All in all, if everything is working, this sounds like a very good deal. If you decide that you like the handling of the camera and don't mind the weight (you'll probably get used to it quickly), you could always upgrade to one of the later models later on and sell this camera for what you paid for it.
Advantages of the Koni Omega include: rugged construction, bright rangefinder, great lenses and fast film advance (which simultaneously cocks the shutter). It is a very fast camera to work with, hence the name Rapid.
I'm a little biased, as a very happy Koni Omega user. It is my most preferred camera (I have a Koni Omega M). After you get used to 6x7, those 35mm negatives are going to seem tiny.
Are you interested in macro? If so, I will tell you about the options, but I think that this post is already long enough.