There are no visas in the quota for this year. You can apply for your H1B visa w/ a provit company on 04/01/09 to begin 10/01/09.
You only get a total of 6 years combined. So if you worked 3 years for non-profit you will get 3 years for the profit. That is your 6 year maximum.
You can work for the Non-profit as long as you have a current visa petition. If you apply and get an approval for a profit company for 10/01/09 then you can work for non-profit until that date as long as it has a validity period to that date or beyond. You can continue and work for the non-profit and take up employment anytime with the profit. You don't have to start on 10/01/09 if you want to work longer for the non-profit and you have a date that has not expired.
You don't have to get a new Hhhh1B visa for the profit. You just go to work for them
when you want after you get an approval. You can go to work anytime after the beginning date on the approval notice, - even 6 months later NOT before.
You cannot get a visa stamp for the profit with an offer letter, you have to have an approved visa petition. You can get a visa stamp for the non-profit and use that visa for entry for the profit company later on if you go out of the US.
You don't have to make this so complicated. If you get approval for the profit company you can go to work for them any time after the approval.
You can only get a visa from the embassy if you have a visa approval. You can get a visa for the non-profit and use if for the profit if it is still valid.