"When I'm fermenting without jackets, like in a food grade barrel, don't I need to worry about temps? I no idea about the right amount of fruit to water, yeast, etc. "
Try not to let it pop up too high on temp, but honestly unlike whiskey wash there is a limit to sugar presence and it wont take off the way a batch of wash with potential for 12% will. I've just used the fresh juice from the pressing and added a wine yeast with esters I desire (think clean aromatic whites) (I once used an ale yeast with apples that worked lovely also). I am sure there are more 'refined' approaches but this is just one simple option. I personally pre-pitch in a dilution.
Pears can have a bit of un-fermentable sugar, so heads up on that, be careful about infection. I am always careful to give a long secondary with fruit and make sure it is done, but careful of spoiling with no cooling abilities.
Hope this helps, if anyone has a more technical approach I would love to hear advice.
Cheers!