A router with a 45 degree angled bit should work fine. You should make sure
to mount the plexi very good. If it vibrates or moves a little bit, it could crack.
Polishing plexi is a bit of an artform heh.
You need to use proressive sanding.. from med grits all the way past like
1600(?). I believe they sell plastic polishing kits with very fine grits...
and buffing compounds.
Ive heard that model makers use that method to make the plastic
windows thinner. They sand them down, then at the last step,
they recomend "Future" Floor Polish, to buff it to a clear glasslike
state again.
Torches can work.. but, its very dangerous. More risky than its worth
I think. If the plexi gets a little too hot, it will form bubbles, and ruin
your piece.