Looking for advice about events

If I were to host an event where I expected 30 or 40 people to show up, what kinds of things should I think about regarding lag and sim use?

Do prims worn on AV's count in the prim limits?

Is there a recommended percentage of prims I should have available for a given number of guests? (I.E. If ten people arrive at the same time on my land, should I expect to need to have a certain number of prims free per person?)

I know that asking people to turn off bling will help with lag, but are there other things one can do to help this?

And, probably the most important question of all, what other questions should I ask?

Thanks in advance for any answers/questions.

Worry more about the scripts they wear than the prims.

Suggestions:
1) ask visitors to remove xcite/sensations sex parts during the event. (most people forget or can't be bothered, so you'll have to follow up by checking them in ctrl+t)
2) ask visitors to remove bling/any scripted clothing and hair for the event. (yes, it's pretty, but you don't want it getting in the way of fun, right?)
3) you might consider asking visitors to remove AO/huds (a lot of which are more worried about flashy and multi-use than affect on a sim)

Just a few ideas, but ones we've found WORK.
Good luck with your event