Yes to the garage. Yes to completely outdoors. We are neighbors. I live in the shadow of Gillette Stadium. Our last few broods have all been done outdoors using just a MHP. We have done March& April. I recall last year while they were a week old it was in the twenties a couple nights. They just stayed under the MHP and slept soundly. They stay inside for a few days to make sure they are OK and for the grand kids to see them up close.
Here is the post that led me to MHP outdoors.
https://www.backyardchickens.com/th...d-in-the-brooder-picture-heavy-update.956958/
Here are couple articles I did on brooding outdoors.
4th time is a charm
MHP in March outdoors
Good luck