For that first part, you can use Purify/Corrupt from the menu at any point to switch between (in your case 80 and 30 health). I tried to balance each encounter differently but I do think this version of Dominion is one of the harder ones (previously it was completely random like The Heap).
As for defending, Dominion does it randomly I think 2/5ths of the time, and The Eye is meant to Sin twice and Guard the rest of the battle (though we should probably change it to a cycle).
We planned to include a final sequence, culminating in a final boss and more happy ending (or multiple, based on which side you killed more), but we cut it at the last minute due to time constraints. I'll have to talk to the team about if/when we want to make a definitive version.
Animation was almost cut, because I spent a lot of time trying to make one specific animation script work and I just couldn't, but eventually I found one that worked, even though it does mean that the animations are a little wonky.
VX Ace was just the version we (I) had on hand. This is actually our first experience with RPG MAKER, and as for if we make more? We'll have to see...
-The Director/Programmer