Store it in the frig, it will last a long time. I've done it for years (I like to bake a little bread every now and then). You shouldn't have any problems with the yeast. You also don't have to worry about it coming to room temp. I like to start with oh, a couple cups almost warm water, 1/4 tsp yeast (straight from frig) and about 1/2 tsp sugar, let this sit for about 15 min to get the yeast going and then I'll add the rest of the water and sugar.