Ok the 32 and 42 series are rainbirds homeownrs rotors. The product youll get at SW are contractor grade.
For the back yard 21 rotors may be overkill but it depends on the shape. If it is a basic rectangel then we could lay out your system and do it with 14 rotors RB 5000 or Hunter PGP's. If you give us more info we will help you with this.
what is your pressure, gpm's, well or city water, service line size. shape of your property?
Thanks,
Pete