I’m still working through a 25kg bag of 00 that I’ve had about a year. Seems fine to me, just been in the sack with the top rolled down. I’m sure it’s degrading to some extent, but nothing that has been noticeable.
It will, but like coffee beans the quality doesn't improve by being stored that long after having been ground.
If you're going for economies of scale, you're better off buying whole grains and and a flour grinder - which is basically my dream setup.
Flour should be fresh, buy smaller quantities more often. Or get grains and milk your own.