Tell ya what… I’ll trade you my 2,500 sq. ft. home for your 6,000 sq ft home!
On a serious note, you may have to get a second hub, depending on walls or other factors that’s pretty spread out. If you use a number of z-wave devices like switches and outlets you’ll probably be okay there as they’ll repeat through the network, but Zigbee repeaters are less common. Motion Sensors (if plugged in) or the SmartThings outlet (I think the new one is Zigbee and a repeater) would be your best bet there.
As far as I know, there is not back, restore, import/export options at all, but on the other hand it’s all cloud based so all your settings are stored there, not on any of your devices (phone, tablet, etc). You can switch to a new phone (which I did about 2 months ago) and everything within the app will be there just like on your old one.