OK, 480C should be plenty. Though, a warning - not all soldering stations that can be set to 480C can actually maintain that temperature when applied to a large thermal mass.
I have had cheapo soldering tips that disintegrated in lead-free, you might want to try something different. (That ugly blob looks exactly like my first foray into the sadistic hell that is lead-free solder, so I think that's what you've got. Either way, the stuff already on the board is definitely lead free.) I use Kester 44 (eutectic)
- don't gasp too much at the price, remember, that's a full pound of it. It's a bit thicker than what Dave and company recommend, but I like it.
Either type of flux will work, and I find both equally convenient, so just get whatever you think you'll prefer. I think you'll find that a lot of things magically start working better with a liberal application of flux