It should keep well if refrigerated (NOT frozen). The "washed" emulsion is fairly stable, the "unwashed" emulsion is very stable (I had some in my fridge for months and it was fine).
Adding a few drops of 10% thymol in ethanol/IPA will lessen the chance of any mold growth. It's best to re-melt only what you can coat in a session - repeated re-melting will likely cause unwanted ripening and/or damage the gelatin. If you're using a hardener, add it only to what you are immediately coating.