check your break fluid reservoir above the brake booster to see if you're losing fluid, but it doesn't sound like you're losing fluid.
Wheels being seized on the hubs is pretty normal from my experience- the hubs get rusty and the wheels just sort of want to stick to them, happens to me sometimes.
If you use a c-clamp to depress the rear calipers on a p5/ES you'll ruin the caliper. The pistons need to be retracted by removing a bolt on the back of the caliper that's covering a gear that you stick an allen wrench in, and turning it (counter clockwise?) will retract the piston.
I did the allen wrench thing... then i scrapped my calipers/rotors and put the full set up from a 2007 mazda6 on my car... which is awesome, but when i put the new set up on the rear rotors rubbed the pads for a while and made a bit of a ringing sound while driving. It went away after a while, so maybe you're will too.
I'm pretty tired right now and i'm sure i could have worded that better, but you can search around for the stuff i mentioned (ruined caliper after c-clamp... normal noise after changing pads/calipers... that wheel being stuck thing) and you'll probably find some guy who wasn't as tired as me answering some other guy's problem eh?
now: me sleepy.