I've been using silicone cake pans in my electric oven for a while and they work great and cakes come out easily and washing then is also very convenient. However I see that there're lots of traditional metal cake pans of the same form in shops and so I guess they are in demand.  Why use a metal cake pan and not a silicone one? 
Depends on how many solids and how much water you have in it. If you've rendered, filtered, and refined it, it should last a few weeks easy.   Note: my mother maintained it never EVER went bad, refrigerated or not. Lot of old time southern cooks will say the same, but they all go through it fast. 