asterisk users - Mar 2006 - Thinking of moving from pure VoIP to PRI - thoughts?

Hello,

For a whole lot of different reasons, I am thinking of moving from pure VoIP
(my DID provider gives me SIP access and my termination is SIP too) to PRI
(possibly keeping termination in VoIP for long distance).  FYI, my business
is Hosted PBX...and my end-points will stay SIP.

Here is the thing: I don't know much about PRI problems, so what can I
expect to have to deal with (except for cost of buying the PRI hardware from
Digium and learning how to set it up)?

In particular, any comments on the following would be appreciated:

1) Using Asterisk to do Fax-To-Email on PRI: does it work?
2) Can I limit the number of lines that a particular customer (that has, for
example 10 Polycom 501) can use at a time?  Can this number be different for
each customer?  What Asterisk functionality can I use for this?
3) CPU load when transferring an incoming call via a PRI to a SIP endpoint,
vs SIP-to-SIP transfers

Thank you,

Mike