first welcome to the forums and yes you can seach in the bar to the right for any questions you have.
now, for your question, the wii and your cellphone are different signals. so they should not interfere with one another. you should not get more or less bar because of the wii.
Depends how far is the wii from the router. before buying the router check the range of the router, now, if you have between the router and the wii, you should consider buy a router with extra reach, just in case.
example, if a router's range its 20 feet and you wii is at 18 feet, buy a router with 25 feet of range.