1. By definition, the perpetual valuation methods are Actual Cost in GP. Standard Cost in GP is one of the 'Periodic' valuation methods.
2. You can import into the Standard Cost field using Integration Manager.
3. Current Cost is updated by Purchase Receipts.
It sounds like you need to have a conversation with a knowledgeable advisor about what valuation method is appopriate for your business. If you choose incorrectly in the beginning and need to change later, it can be messy to clean up.