for chrs, you can have them be any size and yes the frame size stays the same for all frames. WHat you do is use a big frame size like 40x40 and only use something like 20x32 of it for the character and teh rest you use to the frames with his sword or what ever else. As for hotspots, you can have any hotspot size and position. Chrs are fully customizable.
Also, I recomend you try to make the base battle system you want before trying to dive into techs. Take a look at something like
this to see how they made it happen. Just to get you started, that game's battle system starts when you press space in game. It calls the function in main.vc called 'void Encounter (int encountertype)'. see if you can follow the logic of how it runs. It's essentially the same thing as you want to do only they choose to use a different backdrop.
If you have any questions, I'm available on mIRC in #vergehelp and on AIM as actionsketch ^_^