About the partial respawn - something new you could do... that I don't think I saw is scaling the monsters up to heroes level when they come back - for example if you beat some monsters in a level 10 area and then you have to come back to that area when you are level 25 - the partially respawned monsters should also be level 25 now or something like that... so that they don't die in one hit.
I know about this system but... I'm not such a big fan of it. Because I like world cohesion in a game, and it's not really realistic that monsters would "grow" as you grow.
About the extreme mode and extreme grinding in the beginning - don't worry about it - I am sure I will find a way to not really grind (a.k.a secret skills pulled out of my magic bag with magic strategies invented by me)
When you just have... 1 skill to choose from, it's hard to come up with magic strategies. I'm tempted to put that extreme mode and see you suffer (at least early on), mwahahahah!
That said it's really just that, grindy. Monsters at the beginning, like your charas, don't do much, so they aren't really threatening, just require more time, more healing etc.