Best hardware configuration for conference system

We’ve developed an ARI-based application which manages multiple conferences, and is running fine on development systems. We now want to put this into production, making sure that we have the most scalable platform. I’d be grateful for recommendations for optimum hardware configuration.

We’re looking for 80+ users in 10+ conferences (I’m using Asterisk 13 bridge technology), and we’re currently using Ubuntu. All channels will be SIP, across the NICs from third party providers or our own IP phones. We were planning on using VMWare ESx solution - with both the .Net controller application and Asterisk boxes running in VSphere, but it looks from various postings that it doesn’t seem to be a good idea. So, what is the best kind of hardware configuration, should I be using additional hardware cards, and if so, which ones?

Thank you for your help