Help for a novice please!

I have a Vigor 2860 router and I am using the Wifi and wired LAN components.
I have purchased an EE 4GEE wifi router because my ADSL connection is SO bad (central London, maximum 6mb/sec in EC1, nightmare).

What I want to do:

1) Configure the Vigor to route NETFLIX traffic (from my Blueray player which is on a CAT5 wired LAN connection) via EE.
2) Everything else should use the [uncapped but slow] ADSL connection, with the caveat that:
3) My NAS box which uploads backed up video etc should always use the ADSL connection (speed is not an issue for backup)
4) unless there is serious traffic congestion then switch to the EE box.

If (4) is too complex, I'm happy to just have fixed IPs for my Blueray and NAS drive, to route via EE or ADSL as I require.
The EE box is plugged in via the WAN LAN port on the Vigor.

I understand how to configure my devices to give them fixed IPs
I understand the basics of IP address ranges etc.

What I don't understand is:

a) How to configure the Vigor to route traffic as above
b) The relationship between subnets on the two boxes
c) Gateways
d) How to configure the EE box (which does not have a Bridge option) to play nicely with the Vigor and still be accessible (for starters, the IP can't be 192.168.1.1 for example as this is the Vigor fixed IP)
e) How to make sure something weird isn't happening which means the EE box is churning thru its 200GB allowance (could I have caused a misconfiguration so my network was spewing out traffic and using the allowance??)

The EE box has very basic configuration options; DHCP for the local WAN (on/off) and basic IP, gateway, subnet settings, etc.

For context:
The EE 4GEE provides circa 15m/b sec, which means one can watch Netflix HD etc without it always freezing.
However, EE is expensive (£70 for 200GB).
I installed the 4GEE box imperfectly on my network, fiddled with the subnets to stop Vigor complaining and all seemed to work. Unfortunately the 200GB allowance was used within 5 days. This is strange as my ZEN internet provider on the ADSL bandwidth measured an average of 170GB a month usage only once going over 200GB in 6 months. EE claim I used 200GB in 5 days. This seems odd.

HELP! ..and will happily send beers/wine as required to anyone who can recommend a setup.
I really should know how to do this, but TBH don't have time to dig thru the relevant docs and learn what I need to do so!

many thanks,
Andrew