Creating 2 networks with one internet connection

[MassiveJim]

Equipment I have
1 - ADSL modem/router
2 - cable router
3 - Vlan capable switch

currently the adsl modem is connected to the internet, cable routers WLAN port is connect to one of the modems network ports, however I want to introduce the VLAN capable smart switch here and totally seperate the networks whilst still allowing them both access to the internet.

Network 1 uses a server for DNS and DCHP, network 2 currently using the cable router for those services.

 

[MassiveJim]

Current setup is.

Internet comes in via the ADSL router (Asus DSL-N55something or other) which has all my PCs and the DHCP/DNS windows Server attached to it. This is network 1.

ALso plugged into the ADSL router is the WAN port of a cable router (TP Link not 100% sure of model not in the premises at present), this router handles the DHCP for network 2.

I haven't setup any NAT rules but anything connecting to network 2 has internet access without any issues.
I absolutely want to seperate these networks, that is the entire point of changing the current setup.
AFAIK neither router supports VLANs.

I'll be honest I haven't bought the switch yet and reading a few guides suggests doing this with 3 routers, using the WAN ports of 2 Cable routers to create the 2 seperated networks.

I honestly don't know the best way to handle this as I am not proficient at setting up Vlans etc.

 

[MassiveJim]

At the moment network 1 is presumably only able to see itself, while network 2 can see both networks?

Adding a second (third) router would give you more separation. Unless you deliberately change something they'll effectively be isolated.

You are creating a double-NAT situation, but for straight forward internet access it probably won't cause much of an issue. If you're opening ports to allow external access it could be a pain.

If you wanted to get down to a single device DrayTek (amongst others) routers will do port based VLANs. You can configure a different subnet for each switch port and have them sharing the same connection.

Yes that is correct.
does the option of using a 3rd router completely seperate the 2 networks ?
What issues might one face with double-NAT ?

Can what I want to do not be done with a standalone Vlan capable switch and no further equipment ?