@Daggett 

Hey Daggett and Welcome!

After reading over your ideas it does sound possible but can I ask are these going to be cable into each other?   You did mention running a cable outside, so if that is the case then 100% go for it!

However, if you are not intending to cable them together and want to use the mesh, instead opting for a WiFi connection between them I would recommend thinking about installing the EAP225-Outdoors in the Barn and Grain house and perhaps a 3rd on the side of your house external to the others.. .  As these are weatherproof they can be mounted on the external wall to have some better line of sight and should penetrate into the barn/grain also.. best of both worlds!   In the house go for the standard 225 on a ceiling.

The 100m range is going to be your issue, its do-able but not ideal... usually 70m is the maximum hence my thinking of the extra 225-outdoor on your house.. purely for talking to the other 225-outdoors.  80+db is close to dead air space sadly, you are likely going to need to go external.

How much is your budget on this?   If you can afford you could use CPE devices to send the signal between the barn / grain and house.. then use the EAP225 inside the buildings..

Whatever way you decide its going to need an OC200 to control them, enable Mesh on the controller and you can adopt the others from there.

@Daggett 

Wireless Bridging and Mesh are not the same, you more than likely want MESH

Bridging is basically the WiFi version of running a cable between A and B... It doesnt offer any connection to clients (Phones, laptops etc) it just gets the data to the other point and then you can use something like the EAP225 to serve the clients.    Bridges are generally the CPE range of devices.

Mesh is just the ability to have multiple APs connected via WiFi to extend the range and serve more clients.   As you are likely wanting to have Phones, laptops etc in the barn/grain this is what you are after.   Its not the ideal scenario for your setup (the range) but it should work!   the 2x other APs (Barn and Grain) will communicate with the house as "extra nodes" and extend the range to their effective areas.  

You will need the OC200 on the main house, wired into the ROOT (main) Access Point..  that should all work fine for you :)

The links below might help you with this

https://www.tp-link.com/uk/support/faq/2949/

https://www.tp-link.com/uk/support/faq/2283/

1. Get the house OC200 setup first (SSID, Password, Fast Roaming and enable MESH etc) then cable in and power on the House AP..
2. Once its up adopt it via the controller, it will start broadcasting the SSID you set in step 1.
3. Test this  on a Phone / Laptop
4. If OK take the next nearest AP (say Barn) and power it on.   Let it sit for few mins and go back to the OC200.  Look for it appearing on the list of devices with a small WIFI symbol beside it indicting its MESH.. click ADOPT on this.  it will reboot and configure the same as the first AP.  (link earlier shows this)
5. Do stop 4 again for hte 3rd AP

Test..

@Daggett 

I saw the keywords a shed surrounded by metal grain bins. 

If that's the case, I am a little bit worried about this shed. Metal could be a serious factor in this kind of setup. EAP225-Outdoor can be really powerful. But, the enemy of the wireless is the metal. Other EAPs should be good as far as I can tell. Avoid the metal if possible. Try and adjust the plan. 

@Daggett 

Since it is used in UK? EAP outdoor has some kind of DFS channels avail? Try not to use the DFS and use a fixed channel. DFS detected will drop the WiFi pushing. So, use none DFS will make it more stable. 

@Daggett 

https://www.tp-link.com/us/support/faq/763/

How does DFS affect you?

The 5GHz device may choose a DFS channel during its initial state, so client device will not be able to find its wireless network for a while.

If the device is already operating on a DFS channel and radar signals are detected you will encounter disconnection, however the connection can be restored after a while. But you may see the change in the operating channel.

Note:

1. If operating on channel 52,56,60,64,100,104,108,112,132,136,140, 5GHZ devices should detect radar signals for about 1 minute, and it should take for about 10 minutes when operating on channel 116,120,124,128 according to ITU-T Radio Regulations. Wireless client are not able to find the wireless signal broadcasting by the AP during this period.
2. Although DFS give you the choice to use DFS channels but it may be annoying when there is radar operating nearby. To mitigate the effect of DFS you may choose a fixed non-DFS channel if available.