Help replace brakes.

Just want to know what size hex do I need to remove the caliper. I don't want to buy the whole set. And do I really need to rent/buy the 'caliper separating' tool? Or can I just pry the piston back in? When doing so, is it just better to leave the brake fluid reservoir open, or should I open up the bleeder screw to relieve the pressure.

Mine took a 7mm allen wrench. Strangely enough, the last time I did the pads I also installed a new loaded caliper on each side, and the kit came with new studs... three of the new studs were 7mm and one was 6mm! (the threads were all the same though).

Just pry the piston back...loosen the cap on the brake reservoir and make sure the level is low enough so you don't overflow it...don't ever open a bleed screw unless absolutely necessary. If you do this right, you won't even have to bleed if all you're doing is replacing the pads.
Dave