1.)You can editing your profiles details
here.
2.)Posting on the forums. Sending PMs to people by clicking on their user name and then clicking send a PM from anyone's post. You can also search members from the members list. There you can search members and you can send a PM to anyone.
3.)Blog entries are similar to post. People can post comments to you, pictures, etc...
4.)If you need with POTCO you can check out the guides here. I think the mods wouldn't mind you asking them for help either.
5.) He doesn't owe me money. It seems I have too much.