Yes 40 is no problem, u can consult doctor and ask him

Delivery is possible anytime after 36 weeks, so yes 37 week onwards till 40 whenever baby is delivered it's fine. Development is finished by then, and baby just puts on weight. Post term delivery can also happen after 40 till 42 weeks, but it is not too preferring by some doctors.

Well 36 week is better and also in 40 no problem