@SteeldragonMJ 

Hey

I was able to install a R600 into a sky site (dont know why the business choose sky, however!)   But basically they had to use the sky router then into the R600.  

Yes that introduces a double NAT scenario but it did work without any issues. 

Its likely your best option as sky MER / Option61 is a pain to deal with!   Least that way you can configure your LAN / R600 as you feel and just use the sky router for a WAN port.   There is no reason you need vlans beyond the R600 so hopefully should suffice..

@Philbert 

Thanks for your reply. Really appreciate you taking the time to help. I'm new to networking and my knowledge is very limited at the moment but I was under the impression that double Nat'ing was bad and would lead to performance drop. Also, my plan was to segregate my network into around 3-4 vlans. Could this still be achieved with the setup you are suggesting? 

@SteeldragonMJ 

Yes it can be and is likely the best possible setup for you, would imagine its what most people are doing (myself included)

Set your Sky router to 192.168.150.150 or something like that and enable DHCP (or static if you prefere) and connect your R605, this should get the address 192.168.150.151 for example on its WAN port.

Now set your LAN port (R605) to with whatever VLANs, DHCP   with however you feel..   Say  home on 192.168.1.x    Guests on   192.168.10.x     IOT on  192.168.30.x  etc etc.  The VLANs will basically run from your R605 to the devices (via switch, AP whatever you feel)

The only traffic going to 192.168.150.150 will be WAN traffic.  As you cant VLAN wan traffic anyways it will be removed from VLAN (detagged) and fired out via the sky router, anything coming in via the sky router (untagged) will be VLAN tagged again when it hits the R605..  It should all work fine

Basically you can have full VLAN, segregation etc etc from the R605 backwards.. the r605 will be your gateway.  The sky router will really just allow WAN traffic now.

Only thing to remember is if you are port forwarding, you also need to forward on the sky router to the R605, then the R605 to whereever..

Double NAT..  yes ideally you would rather not have it, but in reality its common place and wont cause you any issues.   I have a BT Hub with a R605 so double NAT myself, also work with large education networks and vast majority of them have double, sometimes even treble NAT and its not an issue.  

Performance drop wise, unless you are absolutely hammering the life out of the router.. I would be surpised if you even noticed 1ms of difference.   

@Philbert 

That's great. Thanks so much for that. Puts my mind at ease. I'm away to price up my kit. Lol. 
Thanks again. Much appreciated.