Restoring rusty wrought iron railing on my outside staircase. How many coats of paint* should I do after I'm done priming?

Remove Rust and Old Paint.
Use a paint scraper to remove any loose or peeling paint. Use a wire brush to scrub rusted areas and loosen rust and old paint.
Prime and Paint
Paint the entire surface of the wrought iron with an even coat of rust inhibiting primer for metal and allow it to dry at least 4 hours. Apply two fairly thick coats of rust resistant paint over the primer using a medium bristled paint brush. Use smooth, even strokes to cover all areas. Allow the paint to dry completely between coats.

More tips here, http://www.ehow.com/how_5908469_restore-rusty-wrought-iron.html
http://www.todayshomeowner.com/video/how-to-repair-and-paint-metal-wrought-iron-handrails/

One coat of paint is less likely to chip than 3 coats. Make sure all the rust is gone before you paint, or you will be painting again in a couple years. Naval jelly can get into the corners you can't sand. Sandblasting works well, too.