spare readynas considerations

hello
we have a rndu4220

we have two identical ext usb drives that the nas backs up to each week, ie we always have a reasonably current bu offsite

we saved the preferences? or something (our config) file & also keep that offsite


so just say we had a fire

could, instead ie instead install a rndu2220, load our prefs/config file (that we saved from the rndu4220), & theoretically load everything back from the ext hd that was safe off site. or do i have to buy the more expensive rndu 4 to be able to reload our previous prefs/config file?

if that worked, could we instead buy a diskless rndu 2 & put two appropriate 3g drives in it & then reload our prefs/config?

ie if we are going to have a spare readynas ready to go, can i get a cheaper rndu2 with 2x3g to replace the now burnt rndu4220?

thanks for your help
adrianjt