I'm guessing the mitx mobo and cpu can be reused, along with the hard disk and optical disc drive (if you have it in your rig).
However, a new psu has to be procured if TS is thinking of migrating its contents, as the x51 uses an internal AC adapter psu, or unless you can modify the new rig to take in the current psu.
Temps wise, you have to do research on air flow for the cases you intend to switch to and the likes, maintenance is also necessary to help keep temperatures in check.
I may be wrong, but if you are reusing the current mobo, I think you may be able to create a recovery media first, then when you migrate your rig over, just do what you would do with a factory reset (of sorts) with your rig.
Whatever you wish to do, please do research on your own because everyone's needs is different. There are youtube videos of people upgrading their current x51/r2, or migrating x51 rigs entirely.