Your question is a little bit unclear--when you say "panels," are you referring to the interior skins, or the external segments? Are you planning to remove sections of the external skin, and buck in new material, or just try to hammer/roll the dents out from inside?
In general, as far as order of removal of the interior skins goes, have a close look at where they come together, and this should tell you what has to come off first. As I recall, they are typically overlapping from the ceiling down to the floor, so removal of the lowest panel first is complicated by the overlap of the upper panel.
For the rivets, you will need replacement pop rivets to reinstall the interior skins. These are typically 1/8" in diameter, and you can go with a fairly short length, as they are only going through two layers of .032 interior skin. For the external bucked rivets, check the Vintage Trailer Supply website--they sell solid rivets that have a head size that matches the other rivets on your trailer, but are slightly larger in diameter (5/32"), to fill the enlarged hole you might create while drilling out the originals. You will want mostly the shortest (1/4") rivets, but may also need some 3/8" length ones as well.
For sealing exterior seams during reassembly, use Vulkem (Trempro 635)--also available from VTS.
If you can post a picture of your dent you'll probably get lots of additional tips.