A few clarifications:
‘Delivery Box’ available anywhere means anywhere in the Trading UI. Not Anywhere in the world (unless you’re using a Trading Post Express summon). If you are at a Black Lion Trader NPC you can now pick up purchases without leaving the filtered buy screen. You can pick up items/funds you cancel without leaving the transactions screen. That sort of thing. You can see an order complete and know what item was delivered while you’re still browsing other categories.
‘Get More Gold’ button simply connects to the existing Currency Exchange. It’s not a new feature, just a more connected UI.
250 is still the max stack size used for a single sale/purchase.