Thank you for playing! In regards to some of the stuff you said,
1. Yeah, I've been having trouble making heavy attacks have a use. The main use of them, that is not seen in the demo, is that they are used to interrupt some enemies when they are doing combos or are invulnerable. I didn't want to just give them a straight numbers boost. I'll have to go back and reconsider. Oh, one thing to note too, is that you can charge the heavy while you use the light, though it will drain more stamina.
2. There are like rest sites between levels where spells can be changed. This is also where you can switch companions, vendor items, etc. Hmm.. it sounds like you were using a controller, there are still many glitches with that... >___> And yes LB/RB for controller is used to cycle.
4. Yes you get to pick a MC and the MCs you did not pick are available to you as companions. Each MC will have a slightly different story and choices available to them. Also, ultimately the choices you make may change events down the line in the story as well as influence the ending.
5/6. I wanted the forest to feel a bit cramped, and I can see how it could be annoying with a ton of projectile enemies. I am currently looking into diversifying the enemies that spawn and making them closer to what enemies are like in Secret of Mana and less of a bullet hell. I am also looking into adding an outline or something for enemies hiding behind trees or bushes.
Again thanks for playing!