Ah, Phoenix weather! Gotta love it. The garage will more than likely cook the roaches in summer, learned that the hard way. You might be ok if you can monitor the temps & ventilate the garage in the afternoon. I've had the most luck with hissing roaches, our dubia were a little slow but are doing better. Haven't provided supplemental heat but we keep them in our guest bathroom over the winter so it doesn't get too cold, but not optimal. A smaller container makes a smaller colony feel more comfortable, they like the constant vibrations and heat from others. You might also consider toilet paper/paper towel tubes. They love to pack into those. The egg crate is good to provide vertical space for larger colonies. You might want to put in some styrofoam or something bulky to take up space so that they're more crammed in. Make sure you're leaving frass (roach poo) on the bottom even if you aren't using a substrate. Also, if you aren't feeding any kind of protein/grain yet and just greens, veggies, & fruits they may not breed well and could turn to cannibalism. Good luck!