Congratulations on your beautiful little baby!
It is really hard work doing all three things! You're already a supermum and only a couple of weeks in

I'm so glad to hear that you're in touch with the ABA and an LC. I hope they can help guide you through this.
I agree with Pretty Butterfly - if expressing is not working well, ditch it and try to put her back to the breast at these times instead. At this age it's pretty typical for them to feed every 1-2 hours during the day and frequent feeding is definitely the best thing for supply. The alternative is to try a better pump - some mothers find one kind works much better for them than another.

Try and take as much time out for yourself and bubs as you can - just concentrate on being together and feeding whenever she wants.

Lots of mums struggle early on with feeding, you're not alone

ETA - I may be wrong, but I think the topup thing is about 'certainty' with volumes, rather than actually necessarily being better. You don't know how much she'll get from teh breast, so they'd rather you give her a set amount from the bottle.
That weight gain is fabulous - why not try breast & more breast for a week and see how you go? It really is mroe effective at stimulating your supply than a pump.