To whatever extent possible, I'd like to buy a large number of general purpose boxen that can be reasonably pressed into service for a variety of configurations, rather than trying to overspecify what we are going to do and buy machines that are highly specific to those purposes.
My thinking is that we will be needing N general boxen to do load balancing/squid/apache and then also email and dns on separate machines too I think, and 2 specialized boxes to be database servers. We have one very good machine (when it's fixed!) to be our database server. We will want another one that's not quite as expensive but which would be reasonably capable of serving as a backup unit. If the general profile that we are buying is capable of doing that, then great. If not, then at least one machine is going to have to be special.
Does that sound sensible?
--Jimbo