Taking the PSAT in 10th is good practice and helps a student get familiarized with the testing environment. The one that counts is in 11th. If a student has completed Algebra 2, I suggest preparing for the SAT over the Summer before Junior year, taking it in October to refresh on testing, and then the PSAT right after.
This leaves the rest of the fall, spring, and even fall Senior year to re-test if needed. If Algebra 2 isn’t completed, wait until May/June for the SAT, when more of the material will have been studied.
AMC depends on how interested a student is in competition math. Mine took the 10 in 8th, 9th, and 10th, then the 12 in 11th and 12th, as part of a regional math club she was involved in since 8th grade. Without a deep interest and ongoing involvement/preparation, it’s unlikely to be worth taking. There’s no reason to take the 12 before 11th grade outside of the elite students trying to make AMO/MOP/IMO who have been deeply involved for years.