I tried this in a 4x4, biggest issues were airflow, access, and spillage. Had to mount the can and fan externally. I ended up cutting an extra hole in the side of the tent, using a ducting splitter, and pushing the air through the filter instead of sucking it through.
Spillage was another issue, even using a large tray with large sides. As the canopy grew it became quite tight in there and mistakes were made and stuff got spilled. Water would travel along the edges of the shelf and along the underside to drip from there onto the lower section lights and plants.
I solved this by making a large poly 'tablecloth' over the shelf where the overhang would act like a drip edge and direct any spillage down the sides. Made a watering can extension using a bit of hose and a bamboo plant stake for extra reach too, this was originally to help with watering the upper level without spilling any but was actually more use on the lower level as due to the height and access restrictions it was a on the hands and knees job.
Thought about an automated irrigation system but the drama that would ensue if anything went wrong made it not worth the risk. Accidental flooding would be catastrophic, and adjusting drippers etc on your hands and knees at the back of a 4x4 tent under a low canopy while trying not to damage any plants or lights is a big no from me.
Also I mounted the drivers externally to help with heat management and height arrangements. With the lights so close to their respective ceilings the drivers would get hot, which then required cooling/directed airflow, which was difficult because of space issues, so outside of the tent they went. That was OK for me as I DIY my lights, but for pre-made lights you might need to purchase and assemble driver extension cables etc...
There isn't much room for circulation fans, even those small clip-on models. I went with no fans, and relied on the air exchange from inlets and outlets placed at opposite sides of the tent instead. Worked for me but surely won't for all circumstances. Lucky for you, you have a 9ft height so it might not be a problem especially if you manage your canopy accordingly.
Overall it was a lot of effort and mistake making and experimentation, there is probably a lot more I'm forgetting right now, and yield was pretty much doubled due to twice the canopy, but I ended up with a lot of stuff outside the tent which ate into the space I thought I was saving.
Planning ahead would help, even to placement of cables and multi-boxes in relation to access doors. I found that nearly everything I had tidily arranged out of the way was a royal pain in the ass to get to. Re-setting the surge protector on a multi-box neatly tied to the far left tent pole on the bottom level while reaching between canopy, light, and other stuff while on your hands and knees halfway into a wet tray and tent comes to mind. It's the little things that become annoying to do that end up being delayed or ignored that wind up hurting your yield (I'll do it tomorrow...)
Done a few runs with this setup but ended up going to vertical canopies, which is far superior IMO. No airflow issues, room to move (stand), more canopy/actual grow area, and less issues all around.
