Question about water height (and heaters)

I joined reddit to ask y'all for some input. I am so new to this - wondering how high the water should be in my tank. Right now it is well below the filter output, which is creating a bit of turbulence and some bubbles, which might be a good thing? Also, I is the heater is supposed to be fully submerged? Like the red dial and all?

Thanks for any recommendations you have - I've spent weeks preparing these plants and only just planted them in here. I wanna make sure I'm giving them a fair chance. I really appreciate it!