Simple Question

I have a packet of S-04. I plan on making a 1 gallon batch of cider. My question is should I use the entire 11.5g pack or not? Thanks for the help.

Also what is the ideal fermentation temp? Thanks

Well, you could use the entire pack... or half a pack. The yeast will multiply up to what they can by themselves, so the amount you pitch, to a certain degree, just determines how quick a start the yeast gets. You do want enough so that they can immediately out-compete any other nasties, but a half pack in just a gallon of cider would be plenty... and you could use the rest on the next batch.

As for temperature, technically your packet of yeast should list its survivability range. Beyond that, it's somewhat a matter of preference. You shouldn't really go above, say, 75 degrees, and most people stick between 60 and 70. It's not a hard rule, though. A higher temp will ferment faster, but could (maybe) lead to off flavors (that could probably be aged out). A lower temp will lead to a much slower fermentation, but many feel the resulting taste is better.

Thanks thats what i needed to know. Looks like I need to order my Ranco controller for my chest freezer.

low and slow, just like BBQing. 60F or just below is perfect IMO.

The pack is meant to give a really good start for 5 gallons. In theory, you can use 1/5 of that (1/4 is easier to estimate). If you're worried about competing nasties, you can put 1/4 into a small amount of cider at closer to room temp, and let it sit for an hour or two... result? fully feasted yeasties who are relaxed, rested, and ready, and already have started their next couple of gens of kids. Fine yeast families, ready to ride west in their connestogas and tame the wide open spaces... if only they could get out of their crowded, constrained environs. Be a love and help them... put them on the Mayflower across the wide expanses to the big bottle, and let them thrive. FREEDOM! Commerce. Young homesteaders, eager to start a new life. Ready to eat, compete, replete with by-products. the by-products that are in demand in the outer worlds.

Sorry, got carried away there.