I use the 2 router setup and it works pretty well. My first router is my Vonage router. It handles all my phone calls and has two hard lines coming out of it. One to my next router and one for diagnosing my friends' broken computers. The 2nd router is my TrendNet wireless router and handles all my home network traffic. I like the setup for the very reason you say so that I can hook someone up to my network without exposing any of the computers on my network. Now I don't have the wireless option like you want, but I can see where it would be handy. A couple of things I've learned though...
I have every computer assigned a static IP address by my router based on their MAC address. All the computers think they are getting a dynamic address, but the router reserves specific addresses for each computer. This comes in very handy when I'm trying to remote in to another computer on my network, setting up remote access, or even bittorrent traffic. I have rules that will forward the appropriate ports to the correct computer and it works well.
The other thing is just to make sure that each router has it's own range of addresses to work with. So for example, your first router may use 188.8.131.52 and then your second router could use 184.108.40.206. That way you know there aren't any conflicts.
If you're router can't assign static IP addresses, then you can also have Windows look for a static address and basically it will do the same thing. Just make sure the address you provide Windows is also allowable by your router.