Uneasiness over adding a wireless router

My older sister wants to share the internet connection here and in order to do so, it means adding a router with hopefully both wired and wireless connections. Even though I'm CompTIA A+ certified, I am anxious over this. I do not want to see a change in the use of the net with the computer. I don't want to have to deal with problems a router can present, some of which involve rebooting the device and such. I'd rather have a network switch if it's all the same. I'd like to be able to set it up so that it doesn't even present itself at all - I don't want it to filter anything, I don't want it to do ANYTHING except just decide what connection and what traffic goes through. I also would like to make sure that if I need more bandwidth, then I get priority.

Networking is something I haven't had much experience with, and in many cases it can work well when it does. This is again one of my problems with having Aspergers - a change in routine. Things are fine the way they are now, and I don't need a problem cropping up that creates stress.

Yes, I know, this can be a learning experience. With what I've learned and experienced so far, I'm anxious.