Hello and welcome to the MFK!
Naples is in southern FL, almost as far south as one can get on the west FL coast, same latitude as Miami on the east coast, 2 h away.
We use greenhouse-like curtains and a little bit of aquarium heaters to keep our 25K water at a minimum of 68-70 F in the winters (for the sake of the tropical fish). We use high speed fans and a small water chiller to keep the same exhibit at a maximum of 82 F with vigorous aeration in the warm season (for the sake of the sturgeon, wels, golden orf, Aral barbel).
You can see what we keep in the 25K in our videos on the channel.
As for the koi + mahseer, I've been learning the hard way that not all mahseer are compatible with koi in our 25K. More aggressive mahseer, such as douronensis / soro / Thai rose, Neolissochilus hexagonolepis and other similar ones, perhaps even the stratcheyi, are not compatible long term with timid fish like koi, GSC, sturgeon, etc. as they will bite their tails, fins, body. Among our mahseer, progenious, khudree, malabaricus, and putitora have not bothered our koi and GSC so far in 3 years together.
Black sharks, small scale mud carp, and yellowfin tinfoil barb bothered sturgeon, so had to be transferred to other tanks.
Do not keep aggressive and opportunistic, fin nipping, indiscriminately biting fish, such as purple Labeo, any Distichodus, pacu, and gar with koi. Big no-no.
High fin banded Chinese shark / loach is a cool idea. Beware it cannot handle high temps, over 80-85 F, cannot be precise, but we lost ours in that range.