The whole FAA inspection process took a lot longer than what I had hoped. Expect to be patient with this process! The FAA inspector working with me was not all that familiar with experimental balloons. Naturally he didn't want to approve a balloon contrary to the way they were supposed to be handled.
Things would have been easier if I had built my own basket. Since I hadn't, he wasn't sure how to document the 51% rule. With the help of Brian Boland, Bob LeDoux, and several other people, I was able to hook him up with some other inspectors who had approved similar arrangements.
You can get designations other than amateur-built, and not have to satisfy the 51% rule. There are more limitations on these kinds of aircraft, so I spent the extra time to get amateur-built status.
There are people in the private sector designated as able to do inspections for experimental aircraft. While a government inspection like mine was basically free, going to the private sector will cost you more, perhaps $200. While the end result is same, I'd go with the latter. The extra money is worth the convenience. Those guys/gals will typically meet you after hours, and you can talk openly with them while not worrying about the heavy hand of the FAA.
During my inspection, I had the lines to my basket tangled. It took me 10-15 minutes to get it untangled while the FAA guy waited. If I was paying a private sector guy I wouldn't have sweated that nearly as much.
The inspection was over in only a couple hours or so. It is much easier to inspect a balloon than an experimental plane. My FAA guy, while not being intimately familiar with balloons, had done his homework and asked intelligent questions about my design and construction.
The paperwork was a headache. I filled some forms out multiple times to take care of inconsistencies. For instance, "Paul Craven", "Paul V. Craven", and "Paul Vincent Craven" are all different to the FAA.
It felt very good to get the paperwork done. After a year and a half, it was a huge load off my shoulders.