On the other hand, what I found when trying to set one up was that (like most parties) only about 2/3 of those you invite show up.
My first attempt at a GB, only one guy showed up... so not so much a gangbang. I think I had invited 4 or 5 (wanting to keep it right around that number). When I finally managed to do it later, I ended up with a few more guys that I really needed. By the third try I got it right and invited a couple of extra girls to help even things out. Fluffers are a necessity of any gangbang (that would be extra girls there to keep the guys hard and happy while they are waiting for their turn with you). I'm guessing the most any girl can really handle on her own without help is 4 (1 mouth, 2 hands, and 1 in either her pussy or her ass - but I don't see most women managing both of those and still handling the other 3).
To answer the original question, how did I feel afterwards? a little sore, a little annoyed at the guy who got pissy because he had to wait his turn, but overall happy that I got to fulfill my fantasy.