No worries, glad you're doing your research
As long as you aren't planning a coldwater or goldfish tank then your temperature should be somewhere in the 75-82F range. I usually keep mine 78-80 somewhere in there. Some fish are sensitive to really high or really low temperatures, but all of them mostly just need a steady temperature. If the steady temperature is too low then you run the risk of them getting sick, same thing if the temperature fluxuates too much.
On a nice big tank like yours I think you should probably have two heaters...just as a failsafe in case one goes haywire you still have one to depend on. Two 100-200 watt heaters would do the trick (you want to go for 2-5 watts per gallon so a total of 150-375 is what you want) but since you live in a relatively warm climate 5x probably isn't necessary.