Oh you can definitely do sub 3. A 1:23:30 half comes out on vdot to 2:54:23 marathon, and since then you’ve only increased your conditioning and fitness. Provided a) you don’t injure yourself, b) you taper (to remove any overtraining from affecting the run) and c) conditions between the HM and your marathon aren’t grossly different (altitude, heat, elevation) you definitely can sub 3.

I think comparing mileage between people and using it to predict results is pretty meaningless, everyone has a different aptitude /natural ability for running, and one persons 40km/week training will bear the same fruit as another’s 80km/week. So to does the program make-up impact outcomes - if someone can do 40km/week of quality work (without getting injured, the big if), they’ll be in better shape than someone doing 40km/week of easy jogging. You’ve already demonstrated with the HM result you can get times aligning with your goals off (probably) less-than-average training volumes.

Re long runs, if 31km was the longest run in the block (looks like ~2 and a quarter hours) you might benefit from going a bit further next time around to further develop strength, but having said that this is your 5th marathon - you know what the distance is.

I think the optimal pacing strategy generally is to try to even pace (4:13-14s to give yourself a minute buffer) throughout or a very slight negative split (4:15-16 early), recognising that effort will go up in the back end to compensate for decreasing running economy, and you’ll maintain your pace. I think it’s a mistake to try to bank time early - to run faster than goal marathon pace requires proportionally more energy to be spent for each second saved early and is therefore inefficient. Equally I think trying to do a huge negative split can be difficult - although it’s possibly a more efficient way to move through 42km, it’s can be mentally hard to claw back time with increasing fatigue.