In which case going for the most memory you can afford would be the best option (assuming you will use it). Apple prices for storage increments is a gouge, so will go with external SSD for that
I figure too much external storage and it defeats it being a laptop. Which is why replacing my current internal 3TB of SATA SSDs in my old one (I upgraded to gradually) I knew was going to cost me dearly. I was actually thinking "oh god, no" when they said about the new super fast SSD speed as by brain was converting it into no SSD storage price drops and how much ££££ it would cost me.
And with spending that much on non-replaceable SSD I figured I may as well burn more cash on 32 GB or RAM (but not 64 GB else I'll end up living on the streets in a cardboard box)
Everyone has their own individual limits and use cases though.
Thought for the day: if you don't use SD cards much - voila, extra semi-internal storage! However, it may not be as fast as external depending on connection method and SD card speeds, and currently very fast large SD card cost a lot. But it's at least an option to add some slower semi-internal either now or later. But also I have no idea how far it hangs out the side when plugged in... but you could possibly even file the "handle" off the card depending on it's internals if you find this idea dreamy!