First Ever Grow!! 5 plants 2x4

First ever grow legally!!! Medical patient in IL. Been struggling with humidity during lights on, dipping below 40 before i bought humidifier. thinking about adding another during day to keep humidity higher than 45 or so. all plants seem to be doing ok, the smallest ones have been growing for about a week now, the larger ones are a couple days ahead. I think they are smaller than they should be due to some really low humidity issues early on before the humidifier, like around 30 with lights on. Trying out adding some fermentating yeast for tiny co2, not trying to boost yields or anything crazy, was just concerned passive air intake wouldn't be enough to fully recycle co2 for plants during lights on. I tend to adjust my fan a lot, trying to find my rhythm for humidity during the day. It usually is either on 75% or 100% power, 400cfm, but with carbon filter on, still pumps out decent cfm, just not sure of true output. Any tips for fixing my humidity issue, or any insight for my plant growth at this point would be much appreciated! peace and love.