Re: strings?
I wouldn't put medium strings on an old guitar unless I knew its history. With over 180 lbs. of tension, a medium set could be catastrophic. Best to have it inspected by a knowleable luthier, if it's a guitar you want to keep for a while.
As written above, the size of the guitar's body and it's scale-length are important factors in choosing strings, as is your playing style. I mostly flat-pick, and I strum hard to accompany my voice. I play dreadnoughts, so the medium strings drive the top for maximum volume...which is less important on a guitar with a pickup.
I'm a big fan of both Martin and D'Addario strings, and I usually prefer phosphor bronze. Most of my Martin dreadnoughts use medium gauge, but I have one Ibanez that I string wih lights and two that use D'Addario's hybrid Bluegrass gauge. Coated strings can be very good, and I use the EXP and Martin's Lifespan SP sets. (Due to their higher tension, I avoid Elixir strings.) My advice would be to use regular uncoated strings until you've settled on a brand, gauge and alloy that you like...and then decide if coated strings are right for you.
And it's a good idea to keep you guitar properly hydrated. Taylor has an excellent white paper on humidity at their website. Keeping your guitar in the right range of humidity will help it last longer and sounding great.
Enjoy!
Bill
