1. I won't say that you never get a bit of shine off tape, but it is made pretty matte to avoid that happening. If the lighting is so strong that it is making your tape shine, it would probably also show up the poly rim too.

2. It doesn't seem to work like that. Once the adhesive has cured (afew hours after you apply it) it is water resistant, and you can wash your hair without the bond being affected.

3. This does happen, but only if you leave the tape on for too long so that it starts to deteriorate. I would sat not beyond 10 days. And you are right - this is one problem which a poly rim avoids.

4. The only reason is as not to cut off the graduated front. So if you are cutting a stock piece down, you keep the hairline intact and cut the excess off the other 3 sides. It is less important if you are wearing behind a natural hairline, but it is still worth preserving the graduated hairline.