I'll give it a shot but you are asking for a lot of info
1.The rear panels are the most basic. They practically just sit there.
2.It does not matter which you install first.
3.Carefully take your old ones off and save everything. If you have to use the old chrome strips drill holes for the tabs rather than trying to push them through the panels. Don't be afraid to use a few trim screws to hold down the bottom edge. Make sure you pull the panels way down onto the doors before fastening. Make sure the panels don't stop the door from closing correctly before you decide the location of the panels.
4.Here's a trick I thought of for the bottom of the dash pad when the clips are missing or don't work; Fasten a piece of wire to the tabs that are there to fasten down the dash. You can do this by making a loop in the end of the wire. Feed the wire through the hole in the dash. Pull the wire tight and fasten it up under the dash. This will hold the dash pad tight against the dash. Sounds like a cobble but if you do it right it will work nicely.
Jim