Firmware updates are generally far and few between, and quite often they involve other changes so I definitley would not worry about the receiver being able to have firmware updates installed via RS232. In fact, that port is generally for use with whole home automation system controls.
The 470 doesn't match the 90Ps, so your logical choice for a center would be the 370, unless you also plan to upgrade to Studios for mains as well.
Presence speakers are a waste of speakers IMO.