Yeah you'll almost certainly see high 40 degree garage temps, without a cover for the pond and a lot of heat it will be impossible to keep it warm enough for the RTC and TSN. The channels will survive without any heat no problem in the garage. As far as summer temps it shouldn't be an issue either channels and the RTC/TSN can take temps into the low 90's as long as there is decent dissolved oxygen. I'd recommend some kind of insulation on the floor prior to pond setup just use the 1/2" sheet insulation from Home Depot or something both for cushion and insulation from the cold concrete
I'd expect a growth rate of 0.5-1.0"/month on the Channels so for them to get to 1lb is probably 12 months. I'm currently raising some in a 5 acre outdoor pond and have seen growth rates along those lines. I'd wait until the Channels are 12-14" before introducing a TSN at 6" and wait for the Channels to be at least 18" before introducing a RTC at 6" to buy yourself some time before you have to worry about any Channels becoming feeders.
FWIW TSN usually put on 2" a month up until the 24" mark then slow down a little, RTC can put on 4"+ a month until the 24" mark then still seem to maintain a 2"+ growth per month at least up until closer to 36".
Thanks for the growth rates. That matches what I have seen (I caught them as fry). Are the channels eventually going to become feeders even if they are grown out? Channels seem to be indestructible, I have had some during fishing trips last an hour in a couple gallons of water. Sounds like the cover is needed, what would you make it out of?