[Asterisk-Users] Starting from scratch

[Warren]

I have been tasked with moving our office from our junky old Nortel 
Meridian system to Asterisk.  I will be keeping the T-1 PRI Voice 
circuits for the immediate future.  My current intent is to purchase a 
nice Dell server to run everything, with a Digium TE110P PRI card.  I 
also intend to run some version of Centos as the operating system.  I 
have a mix of Centos 3 and Centos 4 boxes here and would like to keep 
that consistent.

There will be about 25 extensions to start and up to another 10 in the 
next year.  More than that and we need more office space.

I already have ethernet running to all of the locations where phones 
will be, but in most cases only 1 port, which is already being used by a 
PC, so I will likely need a phone with 2 ports so I can daisy-chain off 
of it.

Customization will be likely as we are a technology-heavy company and 
would like to be able to link incoming phone numbers to orders and 
comments in the database for the sales and customer service reps 
eventually.  We have a programming department (I am sysadmin) and will 
be able to write the code to do this wither on the phone or on the rep's 
screen (pushed based on static IPs).

I would like to keep the phones under $300 apiece (well under if possible).

Questions:
(1) Any advantage of Centos 3 or 4?
(2) What phones would be best to get?
(3) Any recommendation on a Dell server?  I was thinking a PE1850 
because of the dual power supplies and hardware RAID in a 1U chassis.
(4) If I get outside sales agents working from home, what would be a 
good phone for them to get to hook into our system as a local extension?

Thanks a bunch!
Warren