1- Point was RTT offers the advantage of quick moves. Awning room does not have that versatility. Since you are giving up the versatility of quick moves why not gain the option of a fixed camp?1 - Yes, the RTT is easy to set up and take down once it's on the truck. The main issue I'd have is getting it on the truck myself and then taking it off myself for every trip... even overnighters. Setting up and taking down an awning room or roof top tent to break camp and explore would definitely take an extra 10 minutes or so... but it would take me longer to install and remove a RTT.
2 - The awning room is tall enough for me to use during the day as a bug/element free room as I please. If I can find a large enough tent that offers me this, and is cheaper than $175 then I would absolutely forego the awning room.
2 - You can find tents with similar head room for around $200. These are not a tents that will last a life time, ie Ozark Trails etc. Since you are not planning on camping in harsh weather a cheap tent will do fine.
Based on my experience with small kids camping you are not going to want to spend as much time moving as you do camping. We always found a creek or pond or something and camped for a couple of days in the same location with short trips to other interesting places. The more time you let the kids have to run around eating bugs, getting dirty and stuff the more they will enjoy and want to camp in the future.
Indoctrinate them now and they will be happy and willing to go with you even into their teen years.