Sales tax will not populate even after VIN. I don't believe sales tax is something that you can lump into your loan if going through Tesla. Someone can correct me, but I think you're on your own. Texas is a franchise dealer state. Tesla cannot sell you a car in Texas, so they can't pay taxes on your behalf like other dealers can. You're technically buying it in California and Telsa is shipping it to you in Texas for delivery. However, your Sales Advisor can probably give you a rough estimate of what that will cost and how to deal with sales tax.
Tesla will send you self-registration packet that you will then need to take to your County Tax Assessors office to pay the taxes and other fees due to the state. I don't know how a Tesla loan would do that without being able to send you a check to cover taxes and fees (which I have my doubts they'd be able to do).
From my understanding and experience, if you want TTL lumped into the loan you can get your own financing from somewhere that can issue you a check for the TTL.
I'm still in the process of delivery (scheduled for 6/17) so I don't know all this for sure. Personally, I've accounted for my estimated tax bill and reduced my down payment to accommodate it.
Welcome to Texas... yee-haw?