This is what I do too. So far, I've had no problems.

I've had fabric starched for over a year (WIP) and it's still fine.
I use regular cornstarch. I try to keep just one project at a time
in my sewing room. The rest goes in plastic bins (starched or not).
I have quite a few starched strips from other projects. Keep a
close eye for silverfish though.

I wouldn't starch it until I was ready to cut it. If you starch it and the fold it, you run the risk of needing to starch and iron again to get the fold marks out prior to cutting. Seems like extra work to me.

You just learned to make a smaller amount and make more if you need it. I always seem to have a little left over and I always have some fabric to iron or a few blouses. After a few tries you will be able to estimate the amount you need and mix that much. You will also learn than you can mix it so it has light body when you test iron a scrap and add more starch to the water to adjust the crispness you want. You can always start light and add more, you can't go the other way.

Starched material will not go bad. I usually only starch as I cut and I have never experienced bugs. Even when leftover fabric goes into the stash.

Storing dampened fabric in the fridge should only be for a few hours to overnight. It may mold if left longer.

Liquid starch will keep in the fridge for a month or more.
peace

I use the concentrate Sta-Flo, 50/50 and haven't had any problems with it "going bad" after sitting in the spray bottle for weeks. I starch my fabrics that I'm going to be using a minimum of 2 hours BEFORE I'm going to use it, then dry it. I also have had the starched fabrics in the plastic bag for 2-3 days and haven't had a problem. If it was going to be longer than that, I would put the fabric in the freezer, then take out when you're ready to use them. As far as the "bugs" such as silverfish, etc., if you don't have a problem with them previously, I don't think you'll have a problem with them now, just because you're using starch. We don't have a problem with them and it hasn't changed because of the starch.

I starch a lot . Yes I have seen the solution start to change color.. it goes from a milky white to getting a tinge of yellow to it and if I spray it on pure white fabric .. the spray pattern will show up as a faint stain. This "stain/discoloration" does wash out with the starch. This happens when the weather gets warmer... so I mix smaller batches. As far as the fabric I have some starched fabrics for years... but I de-humidify.... and no bug issues. So the questions is how humid is your storage area? If its has a high humidity starch as you need for each project.

This is my thought as well. I only starch fabric right before cutting it. Folding it, or even just handling it, seems to me to weaken the starch.

They would get mildewed (moldy) if left in the refrigerator too long.

However, if one put the stuff in the freezer right away and it stayed frozen, it would "keep" indefinitely.