will having a wireless adapter (in the same house) make the internet slower? will it be noticeably slower (even at close proximity to the router) on the computer with the wireless adapter?
It depends, technically it shouldn't but I have tried it and something was fucking up my signal. I have three cordless phones that used the same signal so I had to set the router to use a different channel, but something was still fucking it up, could have been a neighbors phone or something.
You'll be fine just set the channels at opposite ends of the spectrum. 1/6/11. Anymore than 3 you'll run into problems. If you've got 2 set them for channel 1 and the other to channel 11.
Of course if you are using the internet from the wireless computer and the wired one at the same time it can affect the speed of both as you will be sharing what bandwidth you do have.
I used to work for Rogers and many people had no issues at all with a router-type piece of equipment. However what it's meant to do is take your incoming signal and split it between whatever else you're adding to that line so your 40 gigs can turn to 20 + 20 gigs (for 2 connections in total). Huge difference. We offerred something for $10 a month that sent a boost signal constantly to keep the line running at 40 gigs. If you do set up a router and have issues, call your internet provider and see if you can get a plan like that. If it doesn't help you can get a tech out free to check the lines and stuff, if still nothing they'll credit you back and disconnect it. So no harm done. Hope it helps!