It's not a dumb question is it?

I'm seeing a T -joint plus another L shaped joint - where would I put the fans to make sure the air keeps flowing?

Are you asking where to duct your fresh air intake and output?
Or
are you asking about your lighting ducting?

I would rather have 3 rows of tables so you can get around them instead of against the walls

h

I'm asking about it all. The lighting ducting and the fresh air intake from the window and an attic vent output.

If I do three tables and run them parallel- again is that an easier ventilation set up?

If your not running c02, like me, i have a 6" wind tunnel inline fan to suck air into the room. I also have a vortex fan sucking air thru a carbon filter then exiting thru the lights and then outside. Connected to the end of that ducting run is another wind tunnel fan to pull the air out. Faster the air moves thru the lights the cooler they are.
This installation is i feel a basic yet effective set up.
Your set up would work well with this design. When you connect your light ducting together use hard ducting for the 90 degree turns so you will have no tears or rips at the corners from the force of the air.
h