I will try, and answer.
1. There is no limit. If you feel you can handle 10 OC's then by all means go for it.
2. Post frequency I've never done it on this site. On FF.Net, there's always 2-3 people that make like a hundred posts while everyone else is away at work/school...it's kind of annoying when it happens. There will be different areas so I guess the frequency will depend on who is in those areas.
2.2. I'd personally like to use at least a paragraph or two, but I'm not a taskmaster, and I've done enough group RP's where people use one-liners that it doesn't bother me anymore.
3. I have not considered dice.