If the plastic shield you are describing is black, and runs vertically near the back edge of the door, it is part of the track, and comes out along with it, easily, after you remove a couple of screws.

Yes, there is a screw in the front end of the door handle. I think it's a 10mm bolt. The window needs to be all the way up to get to it.

The hardest part of the job is usually getting the old handle unhooked from the linkage rod (which is just enough too short for it to come off easily) and getting the replacement one hooked on.

If you get the new handle on, and it still doesn't work properly (rare) you may have to shorten the linkage rod, which is adjustable for length.

There are small rubber gaskets that go between the handle and the door. Don't forget them when putting things back together.

Yes, these door handles fail fairly often. I've done three or four of them over the years.