Hi PD55,
IMO, the answers to your questions are:
No!
No! At least some of these products will require you to reapply somewhere along the way.
No! Not if you want it to continue to bead water. Some friends of mine bought this stuff years ago that was supposed to protect the paint from UV, etc. Their car quit beading water about 4 months into it's life. The option then was to either reapply the paint sealent or wax the car. They just started waxing again.
A particular brand? Since I have never seen positive proof that paint sealents do anything at all for the long term health of the cars finish and thus have never looked further, I wouldn't know.

Good Luck & Drive Safe,
Steve
[This message has been edited by Intrepid175 (edited 08-28-2001).]