I guess the obvious question here is did you increase your send volume? Are there any differences between emails pre and post, like certain common links having "mktNoTrack" or some...
The conversion will clear out all your data in that field. You'll want to export everything in that column to back it up and then reimport it once you're down with conversion. This...
You're looking for Describe Lead. You can interpolate the display name of the response with {{lead.<display name>}} for the tokens you wish to insert.
Well regarding #2, this is half-correct. You can enable your sales email activities to sync up to salesforce in your sync options: Customize Activities Sync - Marketo Docs - Produc...
The primary thing that you will need to do is create a new role and set of field-level security permissions for your sync user: Step 2 of 3: Create a Salesforce User for Marketo (E...