My experience is limited to low power rockets and about one year into this hobby. I noticed a couple of melted burn marks on a mylar chute after the final flight of the day...and it got me thinking, if it ripped or melted or failed, I would be without the means to launch/recover my rocket. So, I ordered a dozen plastic/mylar chutes from JohnnyRocket and got them within a week. You can trim them to size 12", 15" or 18" and cut out a center hole if you like as well. I prepped one of each size and labled the plastic baggie (half sandwich or snack size) that I stored it in, so I could quickly indentify which was which in my jumpkit/tackle box. Almost the very next launch, I discovered I had finished my Mega Mosquito, but forgotten to attach the chute! Thank goodness I had those spares ready, and in a few moments, was ready to go.
To answer your question about storage, I carry a bottle of baby talc in my tackle box and assure each chute is powdered when made, but also if it gets melted or stored in a warm/humid spot. Though I have been warned not to store my chutes rolled up in my rockets without unfurling and powdering them again before launch, I have not had a problem so far. I find it essential to roll and repack my chute after each launch, so a breeze doesn't try to jerk the rocket out of my hands, or spin while walking back to the launch pad. Once rolled and reinserted WITH RECOVERY WADDING, the rocket is ready for a new motor to be inserted in moments and ready to launch again.
Hope this has helped.