Numerous questions!!!

The threim pops off, Its held by clips underneath. They make tool for removing it but you can usually pull it off without it. Just becarefull not to twist it. You will need new clips most likely.

The stuff in the drip rail is just a seem sealer, You can scrape it out if you like may be hit it with a heat gun to loosen it.

For the inner fender, yes, you need to drill the spot welds tp remove the panel. You can either buy spot weld citter or use a drill bit about the size of the spot weld. If you use a drill bit dont drill all the way through. You just want to drill as much of the spot weld as you can then use a air hammer between the panels to brake the rest of the weld.