Here’s something I thought of recently,
Would it possible for me a NW6, to transplant all my existing side and back hair to the top? Then just get SMP for the back and sides? And just keep a very tight short hair cut?
Don't surgically commit yourself to a trendy hairstyle. It won't be popular forever.
It's not unusual for a hairstyle to be very popular at one time, and then 10 years later it may be viewed as totally out of style. It may even be considered lower-class or unacceptable in a corporate job.
Lots of balding men got crappy transplants in the 1980s/90s because at the time it wasn't acceptable to wear your hair buzzed down very short at a corporate job. A decade or two later many of them were deeply regretting it. Buzzing down became fashionable again in the later 1990s-2000s but now they had transplant scars. And their 1980s-90s transplant work wasn't good enough to make their grown-out hair look very good, either.
Transplants usually do limit your hairstyling options even with the best results. But it helps if you don't intentionally paint yourself into a very specific corner.