Contact your FFL beforehand, to ensure everything is kosher. Different FFL's have a widely disparate schedule of fees. If you don't have one picked out, give your locale, and a member nearby might be able to recommend a shop, or kitchen table FFL, with minimal fees.
If the rifle is from another state, it needs to go to an Indiana FFL that is willing to do the transfer paperwork. Your FFL can guide you on the process.
Depends on a lot of things. Best case scenario: if both parties live in the same state and neither is FFL, seller can package it, take it to the post office and mail it direct to buyer. No FFL needed. If the rifle crosses a state line at least one FFL is needed.