Work in progress - need a few suggestions

[Jimbotronics]

This whole thing started as a "rebuild my 307 project". After pulling the engine I came to realize just how bad the rad support and inner fenders were - so why not change 'em while the engine is out. SO now I have the rad support, both inner fenders, battery tray, and right fender on order. Then after posting questions about rebuilding the 307 another board member pm's and tells me he's got a crate 350 with 25K miles. So weekend comes around and me and a buddy go pick the motor up as well as get to meet a board member (cdowns - helluva guy and has some cool stuff). Engine came complete with edelbrock RPM intake, edel 600cfm carb, and HEI (got 'em off to run through the parts washer). My question is how do I go about painting the firewall before putting everything back, should I invest in an air sprayer (i have a 30 gal compressor) OR rattle can it or ?. I don't know crap about using an air sprayer but what better place to learn than the frame and firewall right? Also, what do i use to get the old crusty, caked on, rubberized caulking off? Sorry 'bout ramble on on on on. btw - this is my first project so i'm learning as i go...