Hi there my fellow country man!
I‘ve been growing outdoors/greenhouse for a few years...
Intake/outtake: I wouldn’t bother, unless ur g-house is very small. My rig is 6’ x 20’
U defo need an oscillating fan , outherwise humidity might go through the roof (maybe buy a cheap hygrometer).
Keep ur pot in pots, in case it gets really hot (I know it’s unlikely in the UK, but u never know)
Don’t expose your girlies to full sun.
Are the Autos? If not, take into account that 12/12 starts in the middle of September, if it gets to cold, then your buds won’t grow...
I always go for Autos meself, to guarantee a crop...
Anyhow, don’t want to tell u how to suck eggs in case ur a senior grower...
Are ur plants indies or satties?
RW