What's size of your PostgreSQL Database?

Dear all:
We are currently considering using PostgreSQL to host a read only warehouse, we would like to get some experiences, best practices and performance metrics from the user community, following is the question list:
1. What's size of your database?
2. What Operating System are you using?
3. What level is your RAID array?
4. How many cores and memory does your server have?
5. What about your performance of join operations?
6. What about your performance of load operations?
7. How many concurrent readers of your database, and what's the average transfer rate, suppose all readers are doing one table scaning.
8. Single instance or a cluster, what cluster software are you using if you have a cluster?

Thank you in advance!