1) Here is a guide on inserting map sprites. If you have too many, this may become an issue.
2) You'll need to repoint the class table to free space, in accordance with these instructions. Here are the known areas of free space. Get familiar with repointing and expanding; you'll use it a lot, but it's not anywhere nearly as threatening as it sounds.
3) Feditor. You'll increase the max index, write your text in a new offset, then write that offset in little endian (covered in the repointing tutorial if you're not sure what this means) in the correct section of the character structure. If you're not sure, use an existing character as a reference.
4) I believe this is relevant to your interests.
General hints: Before doing anything, always always always make backups. You WILL mess up at some point. It's guaranteed. It's not a bad thing. Unless, of course, you don't have a backup. Keep notes of where you put new things and where they originally came from. Don't worry about running out of free space. And use FEU's very robust search feature. It's great.
Also: Gheb? Seriously?