Replacing a car radio is about as complicated as it sounds—that is, not particularly complex or fraught with major difficulties, but often involving some contortion, sussing out of poorly labeled and organized wiring, grumbling when things are about four inches shorter than they need to be, etc.
The few special tools that are needed (mostly gizmos to insert or remove the radio from its bracket, of which there are a few different sorts) are readily available and not expensive. Nice places like Crutchfield will often sell or give you any necessary odd tools and trim bits you need.
An IR remote generally needs to be pointed roughly towards the receiver on the radio to register. That might be a problem with mounting it on the steering wheel. If it happens to use RF signals to communicate, that would not be a problem. I suspect (in a good bit of ignorance) that most are IR.
