You have the basic steps right. A few ideas:
1. Remove the entire lower interior panels. You will need to be able to work over the top of the floor channel to get at the screws that hold the channel to the floor. You cant do that by just prying the lower edge of the interior panel out from the wall.
2. Remove the belly pan? The bottom row of exterior rivets go through the upper skin, then through the belly pan, then into the floor channel. After you have removed the bottom row of exterior rivets, run a putty knife between the belly skin and the body skin to break loose the rivets. You will find some 'hidden' rivets that are under the body skin, that hold the belly skin to the floor channel. drill these out also. I found it easier to remove a couple of vertical rivets on the body so that I could pry the skin out far enough to get at the hidden rivets.
3. Before you try to lift the body, carefully measure the distance between the main ribs, front to back, side to side, and diagonally. Put in 2x4 bracing from side to side and front to back, anchoring the main ribs, and cross brace to prevent racking. These 2x4s will be the lifting points you use to jack up the body.
4. Before you try to lift the body, go completely around the perimeter again, inside and out, with a putty knife to make sure all the rivets are gone.
5. Remove all the screws that hold the floor channel to the floor. use the putty knife to check that the floor channel is completely free from the floor.
6. Now you can start to pry the body up a few inches using a jack, or even just a crowbar and some wood blocks. Be carefull if you use a crowbar because the whole body will start to 'walk around' unless you keep it level.
7. I didn't have any help lifting the body off. I jacked it up high enough to clear the wheelwells, then hitched the frame up and drove it out. This is very scary unless you have the shell well braced and well supported. I left he belly pan attached until I had the frame out from under the body because I didn't want to be working under the frame with the body up on jacks. I think if you had four people, one at each corner, you could lift the body and walk it off.
8. I removed the belly pan after the body was off. There weren't that many rivets in the belly (maybe 50), and I needed the belly off in order to remove the floor. The belly skin was in two long peices, with a lap joint at the centerline. With a little bit of jostling, I pulled the skins out from the rear. I carefully flattened the edges and rolled it up.
I have quite a few pictures. Let me know if this helps you plan what will be your grand adventure.