don't apologize for trying to learn.
what you have will work, yes.
as for what temperature to set it at: that depends on your environment. my temp settings will be different from yours, as will everyone else's. once you get your t-stat, you'll need to play scientist and spend an hour or so letting everything run and periodically checking temps until you're happy and getting consistent readings. it's a bit of work, but once everything is dialed in the rest is a breeze. an IR temp gun will be a YUUUGE help here.
for CHE probe placement: you'll want to hang it down an inch or so above the substrate. how big is your snake btw? depending on size, they might climb the probe so be aware of that and try to anchor it down somehow, as best as you can (NO TAPE IN THE ENCLOSURE EVER). with a bigger snake this won't be an issue.
regarding electricity: well, the CHE won't pull more than 60 W lol, and if it's running full-blast then your thermostat isn't doing it's job. regulated heat sources are much cheaper to run than unregulated heat sources, as their electricity usage is, well, regulated. the thermostat will be pulling the most electricity, but the wattage is listed on the Herpstat website if you need to look it up.