Best wishes! I’m due in three weeks myself.
In my opinion – if you can – I’d express as much as you can whenever you can. You can always freeze it for later.
That said, some women – like me – and pumps don’t work. If I was to believe the pumps (and I tried various) my boys should have starved!! I wish you the best.
There are some treatments that have varying degrees of success for inverted nipples – but you’ve probably checked them out already.