Even if you want to get FSD, it seems to me that the prudent thing to do would be to not include it in your original purchase as that can impact sales tax / assessed value, etc for your car down the line. If I were you and dead set on getting it, I'd purchase it for the 10K after taking delivery.
It's your money and your call to do with it as you please as long as you are making an informed choice. There are lots of posts on various forums that go over some of the gripes people have with the way FSD is set up currently as being non transferrable in any way, etc. It might also be worth waiting for the subscription service to kick in to try it before you buy it. But at the end of the day, It's your money and YOLO, so do what makes you happy.