Orbi & the new Roomba i7+ connectivity

Yes if you had a modem/router combo before and it wasn't bridged, the Orbi will re-configure for 10. address pool. Since you have the newer SB series modem only, I presume you haven't every reset the Orbi thus keeping the 10 address pool. This is fine. It could be possible that maybe if you have not done a reset on the Orbi since, then maybe you can do this as a last resort. 

Yes you set up the DMZ for the 3700 correctly. I was hoping this would help avoid any issues between the Orbi and Roomba however someting seems to be keeping the Roomba from fully connecting. It's possible there is some port issue or someting on Orbi thats stopping it. 

Yes you'll see other wired devices on the 3700 as it's connected client app is searching was connected to it's LAN port thus seeing other devices stemming from the Orbi thru the 3700. This is expected. 

If you decide to do the factory reset on the Orbi, go ahead and turn OFF the 3700 and Roomba for now. Set up the Orbi router from scratch, walk thru the setup wizard. This time you'll get a 192.168.1.1 on the router, You might first test the Roomba to see if it connects thru the router first. Then try setting WPA to disable temporarily. If the Roomba still does not connect fully with WPA disabled and it's services don't appear, then Roomba and NG need to review this and hopefully collaborate and find a fix. Be sure to re-enable WPA2 and AES after testing the Roomba.