Great list of fish...but I foresee a possible loss of at least 10 fish and as fast as umbees grow, not a single place to keep 1 umbee, let alone 6 by the end of summer.
Just my opinions and not trying to rain on the parade, because ALL of those fish are awesome and Id love to be able to keep them altogether as well.
My reasoning/experiences:
Umbees can grow 1-1.5 inches a month and usually by around 6-7 or so inches, they dont want tankmates, especially other umbees.
I recently purchased istlanum from Jeff as well, 4 of them, and the most dominant 1 killed the other 3 in about 12 days. They HATED each other and I wish I would have separated them. They are extremely prone to bloat, as are the beani.
If you house the beani altogether in a tank and the istlanum together in a tank, I dont think youll have but 1 of each within 3 weeks (or even mix them together) and be lucky to have the 1 remaining not get bloated from stress.
I think (depending on their size) that even 3 umbees (undivided) in a 125 will be problematic as well with aggression.
I dont think the cubans, grammodes or cubans will be an issue (again, depending on their sizes).
Good Luck and keep us updated please. Id LOVE to learn that none of what could potentially happen, happened.