Hey there mate!
I've only got three years on you being 23, but I'll offer what help i can.
Now for removing plastic effectively, I'd say use a 230-250 grit paper followed by 800 grit these are Australian standards so might be different there.
What I suggest is, find a heap of sh*t glue bomb that's covered in paint, get a heap of varying grit papers and go for it. Use bondo here and there and let the learning begin.
Hope this helps.