If I file my tax return and claim the standard deduction, can I file an amended tax return later and claim itemized deductions?

Yes, unless you filed Married Filing Separately and your spouse claimed the standard deduction. If this is the case, you both need to amend your returns to claim the same deduction (standard or itemized).

Yes

Yes.

You have up until 3 years form the original due date to claim an additional refund.

like others have written, the answer is yes BUT !!!! unless you have more in itemized deductions than the standard allowance the IRS provides, it would be senseless to even try to itemize

You can always file an amended return.

Yes.

of course, but you may be more prone to be required to prove those items you are now claiming on Sch A

yes

yes if you can justify the deductions

Yes, but then you lose the std, you take one or the other.