fwiw,, and remember your mileage may vary
a 5kwatt alternator would need to operate in the 200rpm range to be
effective, and have a 10 minute rating of 7.5kwatt without burning out to be
classified as a true 5kwatt,, in my opinion.
it is going to be very large in diameter, something on the order of 24 inches
air core or laminate iron core? that is the question
if it were me, i would pull back my horns a bit and go for a very good 500 watt alternator one that can take 750watts for 10 minutes without burnout.
and do it in the 300-350rpm range.
are you able to build a prototype?
with a prototype maybe you get some partners that can be subcontractors to make up
the necessary parts? maybe a foundry guy to do the castings, maybe a guy that works with silicon steel laminates that can get the stator laminations punched should you go with iron core.
the biggest issue i see with this noble project is getting a group of like minded and capable folks to agree on a design and see it through.
from my experience, i don't see that happening working with diy'er types, not that they are incapable (because there are very capable guys and gals) but because they all have differing idea's on how things should be done,, that is a huge hurdle to overcome.
once you get past that one, then you have to get all the component parts manufactured, and then someone has to assemble and test the units,, the first of which will need to go through exhaustive tests, tests that will end in destruction, tests to find weak points on and on.
seriously you might be better off just getting the ginlong alternator, taking it apart and working with the manufacture to incorporate improvments to fit you needs.
reinventing the wheel will likely eat your 50k in a very short time.
then there is liability issues, insurance issues, warrantee and product support issues and the list goes on.
as i said it is a noble project and something you would have to be very passionate about to see it through to fruition.
Even then you have no guarantee of enough sales to cover your R&D, get a return on investment, cover your overhead, pay the insurance, and everything else ,, before you turn a profit.
when it is all said and done, my bet is you can't produce and sell a 5kwatt alternator as described for anywhere near what the chinese get for their offerings.
probably end up costing twice the price.
interesting proposal, i wish you luck
bob g