An IR thermometer with a laser pointer
would be a good thing to have. Point it at the temp sender and see what it has to say compared to the gauges. Useful for all the other temps too (oil, exhaust, water, etc).
If we're going to be gone for more than a few days I'll put the AC into dehumidify mode, otherwise I set it to regular mode, but at 80F. I have four zones and find if I keep the salon units at 80F the staterooms won't climb much higher without their units running, assuming the stateroom doors are left open.
I don't typically leave any lights lit. I do have a Blink XT camera setup. Three cams, linked to the marina WiFi (at the moment). They're simple to set up and their batteries last upwards of 2 years. Careful pointing of them to avoid stray dock motion is the key to avoiding false triggering. If you've got marina wifi it might be worth considering a simple camera setup like this.
And congrats on the trip!