That's a lot of receiver and will certainly do a solid job.
I would certainly lean towards using the integrated streaming capabilities of the receiver, since they are already there. I'm not sure if you can stream one thing indoors, and something else outdoors from their integrated streaming platform. That would actually surprise me a bit. But, you definitely have the option to add a wide array of streaming devices to the system to suit your needs. The ability to play one thing in the main zone and something different in zone 2 and zone 3 is part of what the receiver does, but I don't think this necessarily extends to integrated streaming services.
The integrated amplification should be fine for your outdoor speakers, as long as you are just running a couple of speakers outside. If you are looking for greater coverage of the outdoor space with more speakers, then you may want to add an external amp with additional channels to cover the entire space. But, that's a design decision.
Likewise, using zone 3 for the garage. Plan on an additional amp for the garage space, and then it's up to you which way you go.