AP1 & AP2

Use the same shaft, and for any wedges used with full swings. After a fitting, you might end up with 6-PW in AP2 and 4/5 AP1 or 5-PW in AP2 and hybrid(s) for 3/4 irons. the possibilities are almost endless, since golfers come in all sizes and skill.

I'd probably want the same shaft across the board for consistent feel.

Be sure you get the gapping you want at the crossover to AP2. The lofts are not the same between the 2

I would recommend you get fitted by a Certified Titleist fitter.

It is not uncommon to mix AP1 and AP2S as you are considering and maintain the same choice of shafts throughout the set? What shaft did your fitter recommend?

I was fit like you suggest and it works pretty well for me. I play AP2-716s PW-7i and AP1-716 5i/6i. All with same shaft and specs.

As a follow up to Erik S. who mentioned above to be careful of proper gaping when crossing over from AP1 irons to AP2 within a single set: Good point.
I had my 7 and 8 iron strengthened to help with the slight gap. I did not, however, strengthen my 9i or PW because I hit them much more pure, more often, and really don't notice any gap issue between the AP2 8i and 9i even after strengthening the 8.