I can't recommend strongly enough that you wait until you have your plate holders in hand before you order the glass. Take one the holders with you when you go to your glass company or framing shop and let them help you measure the exact size and thickness. 1/16th will very likely work, but remember to factor in the thickness of the emulsion. Give yourself a little wiggle room. You don't want the darkslide to scrape the emulsion coming and going. Also, it is likely the glass for the 4x5's for be thinner than for 8x10's.
The storage bags sold for film will work fine for dry plate storage. You can make your own storage boxes from archival mat board, cut and folded just like a flat, pre-constructed cardbox box comes.
Fun!
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