Porting from NVP to REST API

Question

I am currently using PayPal's NVP API. And using the below methods.

1. TransactionSearch (To pull in historic and recent transactions)
2. GetTransactionDetails (To fetch detail for each transaction)
3. TransactionSearch using PROFILEID (To get subscription/recurring transactions related to a particular subscription/recurring profile using the Subscription/Profile ID)
4. RefundTransaction (To refund a transaction)
5. ManageSubscriptions (To manage - cancel, suspend, reactivate a particular subscription using the Recurring/Subscription/Profile ID)
6. GetBalance (To get balance for a particular account)
7. MassPay (To send money to other PayPal accounts using the email address) I would like to know and get assured that I won't be missing anything when I port to REST, and will get all the details (including all the fields) that I have been getting from the NVP response.

Question 1
Can you map me to the respective REST methods for the above 7 cases that I have listed?

Question 2
Can I use the same credentials for REST API? Or do I need to use something else? Doing so will require the users to reconnect to my system via some other method?

Question 3
Another thing I wanted to know is, that if the REST API can be used to pull in historic data(data for all date ranges)? Is there any restriction on the user-type or type of PayPal account or date-ranges or anything else when using the REST API?

Question 4
What else do I need to take care of when I port from NVP to REST?

Please help!