Paying 80% of OTD cost with cash vs paying 20% and then immediately paying off 60% OTD…

Sorry for the confusing title!

I a plan on buying a $28k car (OTD) from CarMax tomorrow and I would like to do the minimum finance amount of $5k, so a $23k cash deposit up front. However, my primary bank is fully online (Ally), and my checkbook will not arrive for another week. I requested that they temporarily raise my debit transaction limit so I can pay with my card, but there is a chance that it will not be approved by tomorrow, which means I would have to wait until Monday—and I must hand in my current tags tomorrow. I could wire the money, but that will take even longer.

The salesperson and manager proposed that, if the limit increase doesn’t take effect in time, I could instead deposit my regular daily max of $5k, finance the rest ($23k), and then immediately pay the remaining $18k. In the moment, I did not want to be hasty, so I said I would wait until tomorrow to make that decision.

I did a lot of research on CMs auto financing over the last week and found that, if I pay a large sum forward, I can then contact CM’s financing department and tell them that I want the payment to apply to my principal, rather than my future payments. Both the manager and CMs website said that there are no penalties for doing so.

My question is: is this a bad idea? My only experience with debt is from my FAFSA student loans, which I payed off last year. I need a car asap, and am open to this alternative (if my card limit is not increased), but don’t want to commit to a $23k loan. Would having a loan that large hurt my DTI ratio, even if I immediately pay off 78% of the loan, so I only have 5k left to pay over the next 36 months?

Thank you for reading this far!