I'm also far from an expert but I've used ospho to protect bare metal parts sitting around the shop for over a year with no surface rust showing. I use SPI epoxy and in talking to Barry over there he's very adamant, for good reason, about neutralizing the product before epoxying. He suggested I re-apply ospho and before it dry's rinse off thoroughly with water while scotch briting. On any critical areas such as body panels I removed all the rust and went straight to epoxy. I don't want to chance it. Something to be aware of with ospho is it leaves a white powder film if you don't clean it off before it drys.
I tested a bucket of bolts soaked in evaporust ($24.00/gal) and bigger parts in a storage bin filled with 4 gallons of white vinegar ($2.00/gal). The evaporust seems to work faster but I'm happy with the vinegar on this piece after 24 hours although I have some heavily rusted parts that look like they will need days. I hear you have to watch the vinegar as it can attack the good metal too. It definitely attacks pot metal. Here's a test piece that was sitting half in vinegar to show the difference.