Will opening ports for xbox live to open nat affect the computer to not be able to surf the web and do stuff.?

im getting a xbox and i was wondering if i should use port forwarding,dmz,or upnp for my nat settings because my nat is moderate and i wanna go on xbox live with no problems. also do i have to change the mtu ? and if i change those things will they affect my ability to go online and surf the internet also will i still be able to go online ?