Brake calipers

Brake calipers come "loaded" and "unloaded or bare". A "loaded" caliper already includes the two brake pads (inner and outer) so if you buy a "loaded" caliper you do not need to buy brake pads separately. A "bare(unloaded)" caliper is the caliper only and you need to buy the brake pads separately. If you are changing only one caliper it is cheaper to buy one "bare" caliper and a set of brake pads. If you are changing calipers on both sides it is cheaper to buy only two "loaded" calipers.

Never heard of a semi-loaded caliper. A loaded one has the pads already installed. The advantage is it saves the mechanic time. I prefer unloaded because I do things to prepare the pads to prevent brake squeak. Very few do-it-yourselfers know any of these tricks professionals use. If I had a loaded caliper, I would just end up taking the pads out anyway. For you, the advantage of one over the other would be price.

Toyota is not known to have caliper problems so there is no need to replace them on a five year old truck unless you are having an issue.

Sticking pistons are usually due to torn dust seal allowing water entry. You can try removing the pistons and cleaning it. If it is not pitted, replacing the seals should do.

No special tool required. If the piston is stuck stiff, put something hard between the one that is not stuck and get some one to press the brake pedal slowly with short strokes to move the stuck piston out until it is loose and then remove the caliper to clean it.

Be careful not to overshoot the piston as it can result in the brake fluid spraying out.

You are welcome.

When reinstalling, do not force the piston it. It should go in with minimal pressure. If forced, it could be seated unevenly.