You would want to change your fiancing option to "cash" which would let them know you are not going to use tesla's financing option (which sounds like, for you, its wells fargo).
You also would want to verify what you need to do with DCU to secure that rate (what they require). When you get assigned a delivery specialist you will need to do whatever DCU tells you they need to get you a check for the vehicle. lots of financial institutions handle that differently.
For me, in 2018, I put a large down payment and financed the balance through my credit union (navy federal credit union). Navy federal made it easy, but I already banked there. I signed a loan document, and they gave me a check "not to exceed XX,XXX" that was blank but had a space for the vin number to be put on it.
I paid tesla a combination of my check (for my down payment) and the bank check for the balance. If you want to use DCU you will need to find out how long they will lock the rate for you (since you are not taking delivery of the vehicle right now) and what they will need to execute on the loan.
This is similar to doing a car loan outside of a car dealership somewhere else, with the exception that you typically are not looking at a 1-2 month wait.
