Yes, that sounds right to me!
As long as the hot part does not start a fire, neither one of those is a big deal. The chicks always need to have enough space at the correct temperature, but it is fine if one area is too hot and another area is too cold. The area that is too hot in the afternoon might be perfect in the middle of the night, and the area that is too cold at night might be pleasantly cool in the middle of the day.
I think we've all done plenty of stupid things in life.
Since you recognized that you needed to learn, and you are making sure you have it right before the chicks arrive, I think you're doing pretty well overall
That will probably work.
Larger is always nicer, but I think that's big enough to avoid the most common too-small issues with heat sources.
How many chicks did you order?
Do you already have a coop ready as well?