RCR quality is top notch. If you visit them in Frazier, Michigan, you will be very impressed with everything you see there. Since RCR races their cars, they are race-proven and you can't beat the monoquoque chassis. There is an in cockpit video of an RCR40 flipping at Eagles Canyon Raceway (around Decatur, TX). According to Fran, the chassis suffered no damage...as compared to what would happen to a space frame design. If for track, you will want to get the optional 6-point cage.
The build manual is adequate. A lot of ideas and processes can be found in the various RCR build logs on the GT40s site. The amount of fabrication depends upon how much you want to customize it. You can pretty much build it from the deluxe-plus kit. Some things you can fabricate (ie. optional front clip hinges, door boxes, etc) or you can purchase them directly from RCR.
By reading the RCR40 build logs, you will get great insights.