As far as wood breathing.. I too think that is a crock. Take any guitar and strip off the nitro, the poly, the tru-oil, whatever exotic sounding finish you want and what's underneath?? sealer and pore filler!! The only way to leave your wood that free of finish is to do a light oil finish. Be prepared for a lot of maintenance though
To me, for a project guitar, Nitro is the best value and if you want your instrument to age naturally in a classy sort of way, nitro is perfect. If you're deadset on the hardest finish possible and the most age resistant.. the finishes LGM mentioned are the best, but are out of reach of most project builders. Might be able to talk your local auto painter to shoot you a clear coat for a fee. What's a guitar for them.. they are used to painting things a couple hundred times the surface area..