Make sure you put the conference bridge in the main cabinet if possible (64bit slot).

4.30 to 4.53 isn't a big jump.
You will have to use OSDM with the conference bridge card (at least according to samsung here).

Just do the usual backup of the db, copy the new files to the sd card via card reader (apparantly uploading the files via it tool isn't recommended with 4.53c on os7200 and os7400). then reset the system, flash the lp40 card(s)

Upgrade any other cards (PRI, MGI, etc) if you want, i usually do the MGI cards.

***edit***
You will need a SPNET license if this system does SPNET, as from 4.4x upwards they charged you for this