@KuchipatchiPod I wanted to circle back to say your advice worked! I literally fed it once at night, once in the morning, then left it alone the entire day...when I checked this morning I had Zuccitchi! Woohoo!
No problem! My litmus test for whether a critter is fully grown on those units is how it responds to the default Meal option. If it hates it, congrats, you have an Adult!
I know the answer to your first question! It will instantly let you know when you check their status meter. There are certain ranks you can't get until they're fully grown as the happiness meter is stunted when they're kids.
As for your second question...I think you have some experimenting to...
It really is!
I definitely starved my Shirobabytchi and let it get chased around by multiple ghosts for most of the day and left it beeping for hours...and yet...Mametchi. ARGH!
Good question...
Probably won't go for them intentionally. What I would like to do is figure out how to raise something other than the best character. How did you raise Masktchi?