If it's too nervewracking to brood them completely in the coop, you could also plan on moving them out there around 3-4 weeks (with some heat) as they'll be hardier by that point and will also need double the amount of space.
Just as a general reference, each chick should have (roughly) at...
The brooder is very small - it'll be ok for maybe a week but you need to expand pretty soon.
Since the coop is done I'd suggest you consider brooding in the coop, if you can run electricity out there, or brood in the garage to spare your house from the dust and dander. Temperatures are very...