i was working for a university, so things weren't quite as easy for me, and i ended up leaving the country again, because i didn't feel like working for that place for 6 years to get a green card sponsorship. i did, however, do a lot of research on that regard.
IANAL, so anything i tell you, you should discuss with an immigration lawyer.
first of all you can get a part time H1B to begin with, and work for that company. important note is that i think you can't own more than 20% of the company, since your part time h1b needs to be legally allowed to terminate the work relationship with you(you're an employee). also there is a little loophole here that good lawyers may know.
second, you can found as many companies as you want, you're just not allowed to work for them. theoretically you can work for the second company while your own thing licenses software that the second one creates, ip can also be held by a third party.
thirdly, keep in mind that once you have a work h1b which is not exempt(so unlike mine), you can always switch employers easily. even if you stop working for the employee you get a commonly accepted 1 month grace period(not defined by law, but by whoever processes your h1b transfer application). also even if you lose your h1b you are still exempt from the cap for the rest of your h1b period.
say you lose your h1b on year 3. a company can still get you for another 3 years even after you left the country without having to wait for the cap.
lastly, and this is probably the most important. once you gain traction with your startup you may qualify for an alien with extraordinary abilities visa, o1 or eb1. there's a list somewhere, but basically you have to fit 3 categories of that list.
anyone with more information on this topic feel free to extend/correct anything i have said.
so the things i'd do immediately is found a company or two, and apply for a company tax id. if when you say expire it's year 3 and not year 6, i would immediately apply for a part time h1b. again, double check everything with a lawyer.
good luck.