It’s always difficult to recommend anything not knowing the rider and the intended terrain. I will try and guess based on what you wrote.
For starting, a steel frame is a good choice and all are good enough so the difference between the good brands is minimal. As has been stated: disc ready is ideal although post-upgrade is possible (if not the D’Brake adapter is OK but not ideal).
Wheel size: I think 26 to 36 is the size range for XC and 24-29 for Downhill (I ride 29+ DH and 29/36 XC). 24 is for small riders or very technical riding with trials-like hopping.
Even with short cranks like 100mm, a 24" is just no fun for commuting anything over about a mile.
As to 26/27.5/29, the difference isn’t huge. 26 is great for learning but the tire selection is getting worse…
I think with a 27.5 you’re probably good (assuming you can already ride a little, for the first time it’s quite big).
Maybe also look at finding a used 26".
If you want to do muni and also commute around town, I would consider dual/triple hole cranks (I ride them almost exclusively on my 4 >24 unis), e.g. 110/136 or 127/150 if you want longer (I like short cranks but that takes getting used to). For starting the VCX 100/125/150 are OK, although with time I find the range too big (I like 110s and 136 better), but good on my 36. Most dealers will let you pay the price difference.
I just ordered a Nimbus Muni 24 with the 100/125/150 cranks. I decided I wanted to prioritize learning(both muni and general skills) for the time being and I can still certainly get around. My campus is maybe half a mile across(but it is a hill), so distance is fine. I figure that it will treat me well as I learn and progress and last me until I can properly excuse expanding my stable.