Great job!
Prob yes. 17C deg is a bit below the ideal night time temp. Different strains react differently.
18C is usually the lowest you want to go, and going below 18C might stunt the growth. But ye you’ll see if they like more cold or warmer nights.
And one more ”new thing” you’re going to experience as you switch the lights 12/12 is the stretch phase.
Your veggies going to stretch noticeably during the first ~2 weeks after switching the light schedule. And the greatest way to control and reduce excessive stem elongation is to keep the day and night time temp close together.
For example your tent day temp could be like ~24C and if you keep the night time temp (during the lights off) above 22C, then your DIF is only 2. If you want to take this method even further you could have an equal or even higher night time temp than day time. Its being called equal or negative DIF. That will reduce the stretch for sure.
If it’s your first time growing then it may be difficult to see why excessive stretching is wanted to be controlled. But no worries, take it one step at a time! Incase you want some further assist on it, feel free to tag me any time.
Yes heaters going to reduce the humidity.
I’m having this kind of adjustable mini heater. Basic system; inside is a resistor that heats up and a small fan that blows the warm air. So the warm air comming out from that thing is dry af
But a good exhaust system will reduce the humidity as well if it exchanges the air fast enough.