Sorry for the delay in responding! I've been tending to my mother after her heart surgery.
On the CMM2, I think it is F2 that needs to be pressed to RUN the program from the editor. It isn't very much different from Atto. I know neither platform has robust file handling (as it should be, given the target, in my opinion!), but my preference between the two editors is definitely Atto.
Andddd, my first home computer that I owned was also an Atari 400. I've still got it, too 🙂 My first home computer experience was the first TI99/4 in 1979 (before the 4A came out). Our little, very rural school received a grant for some computer equipment. One piece of that equipment was an acoustic coupled modem! We got to dial in to the University of North Carolina Chapel Hill. For a poor kid from way back in the Appalachian Mountains it amazing!