76-80F -- if you have one with a soil probe thermostat. Othwerwise you'll hve to engage in trial and error and understand how ambient changes impact resulting temperature of soil. in other words, i hope you weren't too cheap to buy the one with thermostat control. Otherwise adjust power / maybe put a towel between mat and tray etc to control temp. If ambient temps change, then your rootzone temp will change too... get a thermostat controller if you don't have one.
This is reference info.. google to verify exact suggested range... soft-stemmed flowering plants will be similar. Since i started growing exclusively in the winter, I've used 76f for a few years now without issue. Far fewer lag behind. Almost eliminated the ones that take 5+ days.. can't recall the last one that took that long but i don't want to overpromise due to faulty memory.
Seedlings? Take off that dome the moment they sprout. the dome can help avoid irrigating before they break ground, but don't provide much benefit after they sprout unless you live in a desert. Great for clones but not so great for seedlings. Even in a very dry climate you'd want it heavily vented. They need co2 and o2...
heat mats definitely improve consistency of sprout times -- not necessarily faster, but you'll have a smaller window of time in which they all sprout. Irrelevant in warmer climates where the soil remains near 76F regardless, obviously.
'oversaturation' isn't a problem if the medium is properly constituted. It shouldn't take elaborate processes to irrigate or prepare. you should always fully saturate when irrigating and of that causes a problem the fault lies in the medium. Half-watering, or worse spritzing the top, only leads to risk of odd drying patterns that train superficial roots.