The bumpers aren't that heavy, but the rear bumpers will try and rotate on you because of the part that extends forward. Either remove the forward sections, or ideally get help, it makes it much easier. If you want to keep them together (which is what I would do and did) and don't have help, I recommend loosening the bumper and while lying under the rear of the car sideways use your foot to support the opposite forward section of the bumper, while using your arms to support the other side as you remove the last bolt.
It is not very hard, but definitely awkward to do by yourself.
As for removing the rear fenders, they are not very hard to unbolt, but depending on what sealant was used will make a big difference on how easy it will be to separate. You also stand a good chance of chipping the paint, depending on the sealant as well. My TR's DPO used silicone and it was very difficult to separate the two. I had to use a hammer and putty knife to separate the panels.
When you say center deck do you mean the trunk lid or the section forward of that with the gas cap. The trunk lid is easy to remove, the center section with the gas cap can't be removed but would need to be cut out and appropriate metal repair applied. If you do end up cutting the center section, make sure to brace the body so it can't open up at all.
Lastly, I would recommend drilling two very small holes (pin hole size) in each panel, mounting plate, fender, etc. Do this in an inconspicuous place. These holes will allow for quick and easy re-alignment of any panel when you re-install.
Good luck