Is Portenta open HW and what about chip shortage. What if we buy 50 of them, and a few hundred in a year?
No clue as I do not know your market. The best thing you can do is check with your potential supplier. I would also check with a potential alternate supplier. Even a few hundred is small volume as they are produced in the millions. My suggestion is buy a year's supply first and see how things work out. Consider doing this with all of the components especially through hole devices.
This would be documented by Arduino, you can look it up.
I understand, but I also worried if Arduino can send 50 boards at short notice.
Did you ask?
I thought that this is a good place to ask
Silly, ask the people who know!
We can all take a guess and be right or wrong. The only sure way is to contact the supplier.
Customers normally order a number of boards for a year, but have monthly deliveries of the number you can actually use. That spreads out your cost over 12 months rather and a big lump at the start. Called cash flow!