If you can find a good, compact 2x12, one could cover a lot and two (4x12) would cover pretty much anything. Same could be said for 2x10 -- and it will vary from cab to cab -- not all 210s or 212s are created equally -- but, generally speaking, you might find yourself wanting for that second cab a little more often.The more I consider it, a 210 8Ohm 400w cab should be about the right size/volume, and can be added to when/if needed.
Although I quite like the idea of a 212, it's hard to find the right cab at the right price.
That said, there are a lot of gigs you can play with a good 2x10 and a vertical 4x10 stack is nice.
Too, don't let me talk you out of a trad 4x10 if it makes sense for you and your son -- I'm just expressing my preference.