I enjoyed Mira Rescue Co. on account of how it actually has/had a major bondage and kink focus, rather than many other adult games that try to appeal to so many fetishes that they end up providing only half-inch-deep content for practically all of them.
Although I adore Magical Girls, I'm personally not a fan of "MILFs." I do see below that it was intended as an example rather than a New Thing, though. Overall, I'd honestly say you've gotten enough credit for this game that I'd at least try whatever you put out next, whether that's a continuation of this, MRC 2, or something new.
(This did remind me that I had yet to actually pay for this game, however, so fixed that.)
On a related note, I didn't answer the poll as the number of "playable characters" is highly dependent on what you're trying to do. I will note that you can, say, have a main character with a party of a few supporting characters - and doing so does give much more leeway with game balance in a turn-based strategy due to more events in a given turn, so if someone is sub-optimal in one way, it can be compensated for by the acts of other party members.
Whatever you decide on, though, I'll definitely request that you continue the trend of "defeat scenes available even on a victory." Not needing to lose on purpose lest I miss content is always nice.