just what it says, it's missing the bmp file for that particular map. THat error doesn't do any harm, but if you want to fix it putt a dummy bmp in that directory
Edit the text file as Ragnar mentioned, find those lines I forget which ones to be exact. But find those key words, I, Fav, etc and replace them with single characters
I'm not sure I understand your question, do you mean that no matter what the max damage will be 500k and nothing more. Or just not display damage over 500k
are you able to patch your client to show errors? That could give a clue, another thing to check is your grfs aren't corrupted in some way I would guess
I don't seem to see a fast way to do it, the approach you're taking so far seems pretty good, if you know which episode was last touched, you just have to modify/remove content