There is a percent complete column, where you can get the progress. In terms of the rate, you'd have to just watch this and calculate something.

SELECT

db.name,

db.is_encrypted,

dm.encryption_state,

dm.percent_complete,

dm.key_algorithm,

dm.key_length

FROM

sys.databases db

LEFT OUTER JOIN sys.dm_database_encryption_keys dm

ON db.database_id = dm.database_id;

GO

In terms of master keys, you have one per database. These should be linked to the Service Master Key, and if so, you don't need to open them. If they are not, you need the password. No way I know of to recover these. If you remove encrpytion, you can drop it and add it back.

In terms of TDE, you might read this, and then document your progress as you go.

https://www.simple-talk.com/sql/database-administration/transparent-data-encryption/