The only thing you could do is move it temporarily and see what your signal strength is. Generally speaking it is better for your router to be higher than your devices connected to it (greater signal strength). But in your case a signal booster would probably be the way to go. This one got really good reviews http://www.compusa.com/applications/SearchTools/item-details.asp?EdpNo=1503198&CatId=4026. Configuring both DMZ and Port Forwarding would be redundent. Port Forwarding = few ports open for specific application (BF) DMZ = all ports open to the internet. Read this:Port Forwarding vs DMZ
A DMZ is far easier to set up than port forwarding but exposes your entire computer to the Internet. Sometimes TCP/IP applications require very specialized IP configurations that are difficult to set up or are not supported by your router. In this case, placing your computer in the DMZ is the only way to get the application working. Placing a computer in the DMZ should be considered ‘temporary’ because your firewall is no longer able to provide any security to it.
Port forwarding can sometimes be difficult to configure, but provides a relatively safe way of running a server from behind a firewall. Since only a single port (or small series of ports) is exposed to the Internet, the computer is easier to secure. Additionally, port forwarding allows you to run multiple kinds of servers from different computers on your lan. (see above diagram)
Many broadband routers have special port forwarding configuration screens for standard applications (FTP, WWW, Mail, etc) and special screens for custom applications.