Hi Simon,
Can't comment on the Air Suspension question but I chose to avoid it when making a similar decision in 2017. That does mean that you would be without some features that are specific to the Premier version. Colin Barber's overview on the Forum's homepage is really useful in this respect for comparison (linked below). It does look like PCS and ACC were both options on the F Sport grade and Premier models, but again, not sure how common they actually are. Don't recall reading much on these features on here. People do seem to like HUD though, which you would also appear to miss out on if going for an Advance model (Sport and Premier have HUD).
There seem to be mixed opinions on the ML system, some even preferring the 'standard' system, which is pretty good as it is. I settled for a Luxury model with moon roof, but was pretty pleased with the spec as I had nothing to compare it against (first car). I do like my music though and am pretty impressed with the non-ML sound system.
I haven't checked prices recently but you may have to up your budget.
Good luck and do use the search functionality which will direct you to other similar threads (which I researched extensively myself before taking the plunge).