Running vB on large site worthwhile?

[nuller]

Hello!

We have decided on using vbulletin for one of our major websites. This site has anywhere between 500 and 1000 concurrent users at any given time and is rising daily. We would like to implement forums into the website, but before we get too deep into developing modifications for vB, there are a few questions maybe some one out there can answer:

1. All of our members have to log in before they would be able to see the forum, we have their email address, username, password and a bunch of other information that could be used on the message board. How hard would it be to integrate the existing users into vB's authentication & profile system?

2. We have a setup of 4 load balanced webservers, does vBulletin use flat files for anything at all or is it *completely* mysql based?

3. How does vB respond to heavy load? I was reading another thread where people were saying there were something like 20+ QUERIES on some of their pages, we have enough problems keeping our database server from not bogging down all of its processors and exhausting gigs of memory. Why so many queries? I find it hard to go past 4 or 5 queries on a page, if I do that I have done something wrong.

4. Does vB support a mysql replication type setup? Idealy we would like to have a list of slave servers and a master it would cycle through.

5. We would like to implement message filtering, there are certain topics, spam, etc that we need to hold to be approved. How complicated would it be just to get something like this into the current system? The filter isnt the big deal, it's the actual implementation.

So the big question is -- can vB handle what I'm talking about or do I just need to write my own software?

Thanks for your time!
Nuller