Received a few questions on this, so wanted to share this info from my perspective.
As most are aware, the only Model 3 being offered is with LR and PUP, however when you get your invitation to configure you’ll be able to choose color, rims, and/or EAP, etc.
With that said, Tesla is constantly building only 12 Model 3 types, i.e. the 6 colors with 18” rims and the 6 colors with 19” rims. Whether you choose EAP, etc. that is a simple configuration since that hardware comes standard.
So point being, when the next 100 or so invitations are sent out, and those are configured, Tesla is matching a car/vin with that style to your order (the part of the process that can take some time).
A lot of people think their car is being built to order per se, and it is to a certain degree, however it’s more like your order is being aligned to match a vin with the color and rims you’ve selected. That’s why some of the M3 owners have gotten their car in 2-3 weeks after configuring it, while the average is 4 weeks (which includes delivery to your p/u location).
Things will get a little more complex once the SR, DM, P, 20” options become available.
Congrats, good luck, and know that it’s worth the wait regardless on what you plan to configure.