Currently, you cannot add module slots to prototypes of the AgriculturalTowerPrototype type, limiting the number of machines we can add module slots to.
The list of machines we can add modules to, as of 2.0.66, includes the following prototype types.
AssemblingMachinePrototype
FurnacePrototype
MiningDrillPrototype
RocketSiloPrototype
LabPrototype
BeaconPrototype
I'm just suggesting that you add agricultural towers to that list. That way, we'd have pretty much everything that can consume or generate items on the list, other than the ones that generate heat or steam. (that would be boilers and nuclear reactors)
Creator of multiple mods, including Quality Assurance - My most popular one.
Go check them out with the first and second links!
I'll probably be wanting or giving help with modding most of the time I spend here on the forum.
Aside from efficiency modules, no module type would have any effect on agricultural towers. They don't actually produce anything, they just automatically harvest plants.