Well, that is a huge mistake on Thunder's part - you can't say "eight of each" and have 13 pros, or have seventeen players in a 16-player tourney. However, I think he said there would end up being 16 of each, although that does not seem to be the case.
20 players, STUDIOS, is not a great number when working with bracketed tournaments - that's a Round-of-32 with 12 byes ... not the prettiest thing in the world. 24 sign-ups allow for 8 byes and 8 Round-of-32 matches, or else maybe just ask for 32 sign-ups. Although without any invites that'll be pretty hard.
(BTW, JohnHancock, most "invitionals" or "invitationals" by the WGT community are not actually purely by invite - they are just more interesting than, say, "tourney" or "championship". However, tournaments (especially ones with unlimited registration) should have invites to maximize the number of people that know of the tournament, as well as to allow you to have some control over the level of talent of your tournament. A lot of top players do not visit this area often; they need to be notified of the tourney to even know of it in the first place.)