Hi IcedCoffee, I ended up calling an SA to ask them about the benefits of moving down to the 18" from the 19" (which will not result in a refund for difference in cost, in case anyone was wondering).
I did voice my concern about the ample anecdotal feedback regarding the 19" being more susceptible to pothole damage, but he did bring up a valid point, it really depends on your driving style and how fast you're going when you hit a given pothole. He also mentioned that he personally has a Model 3 LR that has 19" wheels and he hasn't had any issues with potholes so far.
He also mentioned that, ideally to capitalise on $$$ I should probably look at picking up 18" wheels after-market if I change my mind about the 19" wheels, selling the latter for a little bit of $.
For anyone still wanting to switch from 19" to 18" though, the SA mentioned that it would not impact/affect your place in the queue, nor will it impact the purchase price.