Newbie here with hopefully a stupid question. If I replace the original radio with aftermarket will it still allow the use of the in steering wheel controls?

 

Kind of depends on the radio. A good sgtereo shop/installer should have something to make it work.

 

You most likely need to buy an adapter, I bought the SWI-RC:
Pac-Audio.com Product Details | iPod Integration for your car and More by Pac-Audio - Connecting you to the future
Which works on the biggest range of stereos. The MSRP on that site is ridiculous, I think I got it for $30 on Amazon.
Really high end stereos have this feature built in, so you don't need it for those. Check the manual...