For your flowering plant I would start around 80% and dial it up a few percent at a time as needed. For seedlings and rooting clones you’d probably want more like 20%- 25% @ 24". By the end of veg you’ll probably be around 50%-60%. Each plant will be a little different, but once you learn their language they will tell you what they want. It just takes practice.
Do you have a time of use meter? If so that will save you a ton on electricity. I think it costs me like 3.5 cents per kwh during off peak hours.