Asterisk questions regarding PRI connectivity

Hey I am in the progress of setting up an asterisk system at my location. We will be running full SIP environment, and have about 85 phones. We are going to be connecting it to a 14line PRI and therefore all outgoing call will be using a standard PRI and not VOIP, but all phone to phone / interoffice calls will be VOIP. Are there any concerns Echo problems, voice quality problems when connecting to a PRI, I have only done testing between VOIP phone and no outbound yet through the PRI.

The server I am looking at is a dual 3.2Ghz xeon with 4Gigs ram and 300+gig raid 5 - should this be suficiant?

I have allready takin into considerations for QOS on all of our switches, and isolating our VOIP from the rest of our network VIA Vlans…

What are some things I should take into consideration with this setup.