help with what? you haven't asked a specific question, you've asked us to design your entire project.
you want to create a door controller. you are asking for help creating a door controller. that is too broad of a topic to get specific help with.
break it down into smaller problems, and solve each of them in turn:
- Create a motor controller that can drive the motor in the existing unit, or control the motor via the existing control circuitry.
- Read input from sensors to know when the door is fully open, fully closed, and if there is an obstacle that would prevent door closure. Don't rely on timing, because it won't always take the same amount of time to open & close.
- Listen for signals from the remote control.
- Get a microcontroller to operate the motor controller, write the required software to read the signal from the remote and read the sensors.
- Test it all, fix anything that doesn't work.
- Done.
Minus any stupid errors on my part, that's probably how you're going to want to approach the problem. That's more or less how software projects are done, anyway; one piece at a time.