Re: Router suggestions
Routers with external antennas will make a huge difference, (i.e. ones with screw-on sticks, 1 is pointless, 2 is ok, 3 is better). Similar to Seti, I have a TPLink W8970 (£70), but you can get the 8950 version for under £50 on amazon (last time I looked) which is the same other than it only has single-band WiFi (i.e. 2.4GHz only, not 2.4GHz + 5GHz)
But ignoring all of that, if you have lots of internal walls in the way then the best way to get strong, fast, reliable connections around your house is ethernet powerline adapters (in my case 1 downstairs, 1 upstairs) which then feed into router/switch respectively. You can always attach a simple WAP to one of those switch ports the other end of the house to serve the vicinity.
Hope that helps.