*Edit: Read through all of this, as it got kind of wordy. Then read what bfrye suggested, as well as searching this forum (click on the 'Search this forum' at the top left of this specific forum, or click -here- if you cannot find it) for topics containing 'migrate' OR 'migration' OR 'migrating' OR 'HOWTO'. If you have anymore questions (which I would hope you do, as there's a lot of information on this forum concerning this one subject alone - its one of the more popular, as well as one of the more often updated topics), the please ask away.
Migration is a long and drawn out process, especially if all users aren't on OS 4.0. Simply put, you cannot build up a active BES with the same SRP as a currently running BES.
Have the OS installed on the server, the local administrator permissions set for the service account, the database software installed (if you have it local to the server), and ESM or whatever else needs to be installed - everything but the BlackBerry software.
Shut down the old BES on Friday night after hours and install the BlackBerry software on the new server. Use the same 1) Service Account mailbox, 2) SRP ID, 3) SRP Auth Key, 4) BES Instance Name (this is the name of the virtual server you give - PRODBES11 or whatever; its listed in BlackBerry Manager).
With migrating the database, please see bfrye's or my HOWTO on the database migration; as well as bfrye's instructions on what to do with SQL MachineName table data (this is in his HOWTO for it).
I've moved to new hardware using a temporary SRP and the above method mentioned by myself and I *definitely* recommend the latter. Its an all-in-one-swoop method to migrating.
And to answer your other question about a development server, no. If you put up a BES using the same SRP ID/Auth Key as another, the SRP will be deactivated within a second by RIM, and your production server will be disabled until you contact RIM. You will need to purchase a second BES license for those purposes.
Also, you do not need to be Tx3 to get a temp SRP ID for migration purposes. I've received 3 temp SRPs over the last year alone and we've only been Tx1 (until this past week).