All of the arduino products will basically be the same for this, you just need to figure out all of your inputs and outputs, in which case you might have to bump up to the Mega. The robot platform will be what changes. As for what platform, I'm not sure we can answer the question, especially without some very specific details, IE exactly what is it doing? You say it stops for 1s every 4inches. Does it need to perform some action in this time? Or is the user going to then need to perform some action and then do something to nudge it along? Is it carrying a load and if so how large and heavy? The task itself sounds straightforward , but will probably require stepper motors, probably with encoders built in, to give you precision and feedback, as well as some form of interface.
As for the interface, that will depend on your budget. Rugged outdoors industrial-ish use will require extra money, and finding a premade module might be worth it. Arduino can be used to make an interface (you just need to decide on buttons, LCD, touch screen, etc), but then ruggedizing it is another task, and you have to decide how it interfaces.
For example, you could be building a robot who squirts a dot of paint every 4" in a straight line, in which case you'd need it to be able to carry and squirt the paint. Or it could be a robot that just measures out the distance, in which case the robot could be a foot long and made of cheap plastic.
We need more information and specifically what you are looking for to be able to answer any questions.