I'm curious why you would want to bother testing if the car is parked? Most ECU won't allowed the cars to start unless they are already in park or neutral.
Let me make sure I understand this correctly, you want to build a remote starter right or do you want to built something more of a security lock?
I'm doing something similar but it's a hardware hack. I'm just going to cut the wires for the starter and put them to a momentary switch to start. So when people get in the car they have to put the key in but it will only work all the way up to "on" not to "start" since the wires were routed elsewhere to a switch I have hidden.
I'm no car expert but to lock the steering wheel the key had to be in the lock position then taken out then you manually have to move the steering wheel till it locks right? It's usually not locked until that happens or until the tires move. At least that's what I thought it is for all pre 97's at least.
Maybe I just missunderstood a bit.