Is this correct way to run electric line?

I am going to rewire my garage. Right now, there is only one receptacle and one light in the garage so I am hoping to add more lines to make things more convenient. I am planning to have a 20 amp circuit breaker, I will run armored 12/2 wire throughout this project from breaker onward. I am planning to have 2 -20 amp GFCI receptacles. A separate regular 20 amp receptacle for a garage door opener. Two motion detectors , one on front and one on rear of garage and single pole switches for each of those. One separate indoor light on a single pole switch and one 3 way light , I will run armored 12/3 for the 3 way switches. Does this all sound practical and feasible? Also can I use 15 amp switches and receptacles or do I need to us 20 amp? Thanks for your help.