As far as problems with neck tension if guitars are left tuned to pitch, my advice (I've done setup work "commercially") is that if the guitar isn't going to be played, then slacken the string tension a peg-turn or two as it can't do any harm.
If the guitar is to be played rather than collected though, keep it tuned to pitch because if the guitar has been kept strung below pitch for a week or two, when it's pulled up to tune the neck will take a little while to settle into the "proper" relief curve and won't have stable tuning until it's settled. Not a situation you want to be in at a gig.
Being more of a player than collector, I just keep guitars tuned to whatever pitch I play them in, apart from my spare vintage floating- tremolo Strat where I back the tension off to ease the trem springs and pressure on the bridge screws a little.
I've a Tele that's been strung 11-48 for over 25 years with no problems, and an ES-135 that has spent over 15 years tuned to open E, 12-53 or 13-54 strings, again without problems. Mind you, that 135 neck is like half a baseball bat.
As for string breaking, I've acid sweat which destroys the plating, and like Danny find a set does 1-2 gigs or a few weeks regular practice and that's it, unless I want to play on rough black wire.The bridges on my Fenders are so corroded they look like expensive Fender Custom Shop "relic" ones.
The way I avoid string breakages (not one while playing in the last 30 years, though a few while re-stringing) is frequent string changes, and close attention to getting the nut and saddles set up correctly and without sharp edges and with a good string angle behind the bridge. I also lightly lube (nut sauce) the saddles, string holes in the bridge plate, bridge pivot points, nut and string trees on vintage trem-equipped Strats. All these points introduce bends which are stress- risers and stress-risers are prone to fatigue fracture.
As strings get older they become more prone to breaking, and also increasingly difficult to get in tune and keep there - intonation also suffers. Steel under tension fatigues and gradually loses its ability to give a predictable and steady response to a given strain. Eventually, rather than being springy it goes "plastic", stretches easily and keeps going flat, at which point forget any hope of keeping it in tune.
Old strings also suffer from the wraps wearing against the frets which causes irregularities in the winding which also does nothing for pitch stability or intonation. If you look between older strings and the frets you might see "dents" in the string where this has happened.
Old, corroded or dirty strings will also wear frets and fingerboard faster, and the moisture in the air is enough to cause corrosion. Strings are (relatively) cheap and easy to replace - frets aren't.
The strange thing is I often play with fiddlers who seem able to use the same set of plated steel strings for many months or even years. Same with bassists, where wear to the wrap caused by frets (and vice versa) rather than corrosion seems to be the biggest enemy.