get a tiny true extractor fan ... something like this :
it will be the last one you need in your size space. it's the smallest available.
that's a 4 inch. pic is from when i was in the middle of setting up the veg space. fans are sized by the inlet/outlet, and the cfm. i don't exhaust my veg space to outdoor.
the fan is adjustable.
allows you to control the cfm and rh% if you adjust careful.
you can see both the exhaust outlet and the speed control on the outside of the space here.
don't worry about the rh%. it'll spike in veg and flower, then you'll have the opposite issue. spending on a humi for a single plant isn't worth it. it'll be fine. i routinely start and grow in 10 - 25% rh with no problems.
just water / feed correct and walk away.
i'm running veg currently at 23%.
did you get a new light ? give us a pic ..
where you set height and dimming will depend on the light. theres a couple simple approaches.
edit : i also have a filter on the end of the fan attached for odor control.