@kurkurkur 

I am a big I fan of the 225-outdoors.

Think we need more info about the structures you are trying to cover, ie just outside, or inside, or both?  Looks like a lot of greenhouses, but possibly also some metal roofed/walled?  Metal walls are a real problem, a lot of wet foliage is also an issue.  Also, need to know if AC power is available throughout the site, or just certain structures.

  @kurkurkur 

You'll have to do some empirical testing to figure out what your coverage will look like on the ground and that will determine how many APs you are likely to need.  Some thoughts for you:

-  keep the access points high up and away from large metal objects

- wherever possible leverage the ethernet port on the meshed AP 225-outdoors to create a wired hop to next downstream AP

- try not to exceed 3 hops or 3 neighbours on any given AP in your design

- maximize your abilty to wire APs as much as possible

- vinyl structures will be easier than the metal roofed ones (require fewer APs) to cover

- research which 5.8G channels are allowed the maximum power in your region, use those keeping in mind all APs meshed together must be on same channel

- I expect you could use the 2.4G radios exclusively for access, and leave the 5.8's dedicated for the mesh/backhauling

There was another recent thread from a forum member with similar outdoor broad coverage requirments, do a little digging on this forum as you aren't the first to have this kind of design challenge.