Welcome to the forum! NE Cheese is convenient, and has a wonderful resource of recipes, but as you gain experience you may want to explore additional suppliers - as I recall, NEC mostly sells packets of their own composition, which work just fine - but are not necessarily the most cost-effective way to go. I prefer to buy bulk packets of various cultures and make my own blends; this also allows room for experimenting and fine-tuning. As John (Duntov) said, keep the cultures dry and in the freezer, and they will last a long, long time.