First, polymer clay needs
no sealing at all. You can do it if you want to give gloss to the surface or to hold little thingies on its surface, etc., but polymer clay is not like air-dry clays and is waterproof for all intents and purposes all by itself. In fact, lots of experienced clayers never even use liquid finishes, or not that often, or they get any sheen or shine they want on the clay in other ways (see below).
If you do choose to use a clear finish, just be aware of their characteristics... for example:
...permanent "white glues"
--including thinned ones like decoupage mediums (ModPodge & others) and dimensional ones like Diamond Glaze, etc-- will have a fairly "soft" surface even once they're thoroughly dried so they can absorb later humidity (or actual water) somewhat easily... if the finish is continuously submerged in water, or just enclosed with no air circulation, the water will also get under the glue and begin to cause the finish to separate from the clay (especially if the glue never dried thoroughly in the first place --each layer too) ... it actually takes about a week for most water-based sealants to "cure" as well as just to dry for most waterproofness
...the old version of Sculpey Glaze
was also susceptible to that, especially when thick (but the new version of Sculpey Glaze is a polyurethane so much better)
...clear "acrylic mediums
" (for mixing into acrylic paints) and some other
clear finishes will also be susceptible to later moisture in the same ways and usually more scratchable
...better finishes to use for polymer clay are clear water-based polyurethanes
, clear acrylic fingernail polishes
, and certain floor polishes
like Future and Mop 'N Glo (Future has been renamed "Pledge With Future Shine") --those will also be less scratchable than the softer finishes as well as harder and more waterproof, though the floor polishes will be thin and not UV-resistant
You have some options now though:
...if they're fairly smooth now, you can heat them in a low temp oven for awhile (either the white glues or certainly the Sculpey Glaze--old or new version)... in fact, even when clayers use something really tough like polyurethane or Future as a finish, they sometimes "rebake" it on the clay for 5-15 minutes at 200-250 F just to further "harden" the finish
...you can also just soak them all in water for a day or so, then rub off all the (now-rubbery) finish and start again** ...sometimes soaking in ammonia, or using rubbing alcohol or acetone, is even faster for some things (see link below for details, under > Future > Removing)
**After they're bare again, you can use a better-quality finish (and let it dry thoroughly, and/or rebake)... or you can sand-and-buff to get your sheen or gloss shine... or you can apply a clear paste wax or Vaseline to get a sheen... or you can leave them the way they are.
There's lots more details on all those finishes, and more of what I've mentioned above on the Finishes
page at my site:http://www.glassattic.com/polymer/finishes.htm
As for storage, first I'd let all "sealed" pieces (or any that you've completely painted over with acrylic paints) air and sit out for at least a week (if the air is cold and/or damp, even longer).
After that, you should be able to put them into little plastic bags, but especially if you don't use one of the better finishes, leave at least a little opening in the baggie. Or just store them unwrapped but in a safe place and with at least a little air circulation (probably most common).
There are all kinds of ways that clayers store their raw clay though and their cured pieces, and there are some materials that clay should never be stored in contact with. You can read about those things on my Storage
page and I'm sure others will have their favorite methods too:http://www.glassattic.com/polymer/storage.htm