|For information on how to add a second router to your LAN, click on my name above in my response and read my "how-to" guide titled, "Add a second Router to your LAN"|
You'll want to use the "LAN port to LAN port" (version 1) scenario for connecting, and configuring the routers. This should allow you to still run the VoIP and TV from the 3801 router.
to add more IP addresses in a home network
I'm not sure what you mean by this. I think you mean, add more available ports to plug more network devices in. If that is what you mean, your second router likely has 4 LAN ports giving you a total of 6 free (keep in mind, you will be using one LAN port on each router to connect them). If you need more than 6, it would be worth your while to buy an inexpensive switch that has enough ports to do the job. You would connect it to a LAN port too.
If you need more addresses, then you just need to adjust the DHCP scope on your router. Most every router I've used by default uses .100 to .199 (199 available addresses) in it's scope.
existing DHCP Scope = 192.168.1.100 to 192.168.1.199
You can adjust that by logging into the router's management interface and changing the scope to add as many more addresses as you need up to a grand total of about 250
new DHCP Scope = 192.168.1.50. to 192.168.1.240
It is not only, not necessary to run DHCP on both routers, it's a lot better, and simpler if you don't. You shouldn't need more than 250 addresses which 192.168.1.0/24 gives you.
Keep in mind that static IP's (like the ones you'll use on the LAN side of your routers) need to be outside the DHCP scope.
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.