the 4-strokes are even more expensive to repair/replace.
What is your experience in manufacturing and precision machining? Have you managed a company before, or acted as a liaison between end-user and supplier in any official capacity?
I don’t mean to discourage you, but this has all been done. KZ engines were an alternative to the Honda engines – those are now even more expensive.
Your best option is to learn everything you can, figure out your budget and buy the setup that fits that budget.
I have an old 2008 Intrepid kart with an old TM K9a (KZ engine) that I run with Woodbridge. I’ve mostly pieced it together with NOS parts that I can find for sale on ebay and here. I’m not competitive with the front-runners, but I have fun, and that’s all I’m really looking for.