I would agree and go with the tri-band version especially if you have a quick internet link and bandwidth heavy usage / multiple devices. You don't want to be sucking precious bandwidth from your operating band - just for backhaul (if connected wirelessly). And yeah, I think personally I'd try for the 1x Router and 1x Satellite initially with the Orbi as you can easily buy another Satellite should you find a dead spot, however the quoted sq.ft coverage of the tri-band models is pretty decent (quoted coverage up to 5+ bedrooms and 4,000 sq.ft for the RBK752 kit).
For info my bro lives in a detached 3 bed with just a normal crappy ISP router in the corner of the living room downstairs and he gets WiFi upstairs no problem so the Orbi units (being superior and quite large) shouldn't have an issue if 1x is downstairs and the other is upstairs. Obviously all houses are different.
Yeah that 30ft figure is their quoted distance for placement but if wired between the two units it could be further away. But I mean 30ft (9m) is quite a distance. I use mine wireless and don't have mine that far apart (mainly due to the stone construction) but also because you have to remember the backhaul channel needs have good connectivity with the other unit and I believe the backhaul channel is always 5Ghz (so even if you had them far apart and had good 2.4Ghz connectivity, you might find the backhaul being 5Ghz changes from "Good" status to "Poor" status in the GUI). So because I have mine closer together I reduced the 2.4GHz power but left 5GHz at 100% (as 2.4Ghz travels easier through obsticales and was causing flapping /mega node overlap).
Just looking the kit I have (RBK752) is £389.99 at Netgear and also from the Rainforest company and might serve you well. You could always return it via the Rainforest company if you weren't happy due to their extended returns. But do what you feel is right and what works for you.