|I wondering, though, if the G devices will slow down the N router?|
People always wonder that and that simple answer is no, G will not slow the N down.
I've been working with computers for a long time now and if there's one thing I've learned, it's to always follow the KISS principle. Setting up dual routers when you don't have to is adding a layer of complexity you do not need. It means more time and effort to configure everything and if something breaks (as so often happens) it means that much more stuff to have to look through to troubleshoot the issue.
If you feel you absolutely have to make your home setup more complex than it needs to be, feel free. But simply put, it's unnecessary if your N router is backwards compatible to G.
I guess my "dream setup" would be to be able to have two separate networks where I could choose either the G or N router depending on the device, and set the G for G-only and the N for N-only.
Look, this is very simple. If you have an N adapter on your laptop and an N WLAN is available, you connect on N. If however, your adapter is G capable (most are) and there is no N but there is a G WLAN, then it will connect at G.
G cannot connect to N but if your WLAN device is N and G capable (most are) then it can connect to said device at G.
So your "dream setup" is actually how things work without having to "set" anything to G only.
Remember, by design, all network adapters always connect at the fastest possible speed, not the slowest
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.