Heater core is out but questions remain.

[In The Ten Ring]

Yay! The heater core is now out but I still have some questions.

There were some leaves and pine needles in there, can I just use a blower to flush out anything else in the ducting?

The fan cover is riveted on in places, is it OK to go back with a bolt, nut and lock washer?

Do I need to paint the fan itself?

What sort of caulking do I use to put the cover back together?

What sort of caulking to put the assembly back onto the cab?

Where can I get a new rubber flange for the fan part?

I'm taking the core over for a royal flush and pressure test tomorrow, I"ll get a new one if need be.