FWIW, one set of opinions:
It's probably time for me to send a follow up email:
I would say it's too long. "Busy CEO/founder" types want brief (as in "2 maybe 3 words") prompt follow-ups. (Again, this can only be an opinion, that's my opinion.)
What should an effective follow up email say in a situation like this?
Unfortunately, absolutely nothing.
There's not a chance you can "language" a CEO/founder type. It would be like trying to - you know - give a presentation in your turtleneck to Steve Jobs" you know?!
What points should be highlighted.
Very likely, they won't be read
Should it be a sales email - trying to sell myself,
No hope there, the CEO/founder type will just gloss over such bumpf.
or should it just be inquiring about the application process?
IMO it should be a straight-up, blunt - yet of course absolutely polite - reminder.
In some sense you can indeed adopt an almost familiar, "I'm already working for you" form of address. After all, this aggressive entrepreneur type WANTS folks working for her/him who know how to get things done and know how to work with her/him.
It is very hard to pull off. (And again, unfortunately, IMO waiting two whole weeks with a "Busy CEO/founder" type is too long.)
Some example texts:
Steve, Fattie here, regarding the amazing Ion Cannon project, any news? Cheers
Steve how are you, chasing you regarding the incredible plasma bluetooth job, kindly Fattie
Steve. Thanks for the amazing interview 13th, just following up, kindly Fatster
Do note that they KNOW why you're writing, so bear that in mind and don't pointlessly explain.
In rare cases you can bring new factual information, if so do it (promptly)
Steve, Fattie here, regarding the amazing plasma bluetooth lead you interviewed me for I did in fact release V2 of my plasma library, I'll let Jane know as well. Hoping to hear on the job soon! Very excited on this end, kindly Fattie
"Should it be a sales email - trying to sell myself, or should it just be inquiring about the application process?". Definitely, you should have sold yourself enough in the interview. At this point, you should not sell yourself again in the inquiry email, and should simply inquire about the decision from the CEO.