My opinions;
Q1. I preffer spoilers and highlight when adding important information. OOC tags I mainly just use for explanation of rules or for in game notes.
Q2. No, I don't find myself editing players posts.
Q3. I typically keep everything public. I preffer a team/group attitude so I typically shun private stuff or mails about ingame actions from members
Q4. I haven't really found a need to use this option. You can always just cut and paste. But I would figure if as a moderator you wanted to split a players post for ease of movement you could use that option.
Q5. I've always allowed players to use whatever formating they like. If I want something to look a certain way, then I will set it up for them to copy and paste.
Q6. Signature is members based, it's for them to express something they want to express.
Q7-Q8. Not sure, havent looked that far yet.