We have carried two kayaks on rooftop racks for many years so here are some ideas for your consideration. Our kayaks are 14 feet Current Design Kestrel so a little shorter than your kayak. We used a BMW 3 Series to transport the boats and we now have roof racks for the Tesla to do the same. When I first installed racks and mounts of the kayaks on the BMW I intended to use the front and rear towing rings as tie down locations but instead I placed an extra webbing strap around each boat and around the roof rack cross bar. This was doubling of the straps that came with the J mounts. In tests on the highway at speeds around 75 mph the boats were stable so I never used the front and rear towing rings. I plan to double strap our boats on the Tesla. Doubling the hold down straps at the front roof rack cross bar is all that is required for our boats.
If you want a bow line to the front of the Tesla consider popping off the plastic nose cone when you are transporting the kayak. There are frame supports under the plastic where you can mount cleats or tie down rings. The plastic nose cone can be stored in the trunk and the loss of smooth air flow will be very small compared to the drag of kayaks on the roof.
On a different topic but related... I was worried about 12V battery failure and needing to remove the nose cone without any tools available. I solved this with two small pieces of webbing that are tucked in at the upper corners of the nose cone. Pulling in the webbing releases the corner clips and the other clips follow easily. I feel that the nose cone was meant to be removed and in your case that would have an added purpose.
Just some thoughts for your consideration.
