Shaved head look after FUE 1.5-2mm length - what results do you expect me to see I’ll be having appx 3500/4000 grafts taken.

3500-4000 is rarely enough to cover an entire balding scalp. My suggestion is to focus the majority of the grafts (at least 3000) to cover the frontal forelock and hairline, and then the donor area can be re-evaluated to see how many grafts could be available to cover the crown (vertex).

Numbers don't guarantee results. It's the doctor and his team that provide great results.
A great doctor with an experience team can achieve far superior results will less number of grafts than an inexperienced doctor with hired traveling techs promising high number of grafts at a bargain.
Remember not all grafts will take. The experience of your doctor and team will ensure high percentage of grafts surviving. The experience and artistic talent of the doctor will ensure a natural looking hairline.

With 3500 to 4000 grafts and the hair that you have now you'll certainly have a more filled in look. However with wearing your hair short you may be at risk for having the FUE scars be visible. A little less than 1.5 mm length of hair is what we use on the ARTAS iX to harvest hair and that is pretty close cut to the skin. With wearing your hair very short you do run an increased risk of having the polka dot scars of FUE be more noticeable in the back than if you wear your hair longer. I would try different guards on your clippers that you use to shave your head. The #1 guard leaves hair 3 mm in length on the Wahl clippers and the next one down is the #1/2 that leaves hair at about 1.5 mm in length. Grow your hair out after the procedure and then experiment with what lengths best disguise the FUE scars but still get you the length of hair you want. Best wishes on your Hair restoration journey!