I've been using simple adjustable rods from my first build and don't think I'm going to change that. I still have my first mandolin and never needed...
Agree with Greg.
You may want to steam the dent before filling. Have a look at frets.com on repairing dings. Frank mostly fills with thickened nitro...
The posts are standard hardware store item. Search for allen socket set screw 5-40 thread. You will probably have problem fingd them in small emough...