You can place fan out of ten with the reducer on the inside and connect to thatthose reducers are actually quite long so its not like the od will make a difference since the duct wont pass through the hole just the reducer
Try 5 2 gallon buckets ( homer buckets), they’ll fit in just fine plus its more like 3 gal of soil that fit. In them. Study and around 3 bucks a bucket
Theres not much more clearance really, so stretch may be an issue.
Like diggity said you may have over done it.
Heres a 4x8 i filled out under a 1k (4x6 really since i had fans and an ac like yours in there)
I see you have an air cooled hood, i went as close as 8 inches under the hood with only...
You have a nice sized room, but i think you may have over vegged a bit.
Itll be hard for you to walk around though to manage everything..
Nice work by the way