Same network on AP?

All Airports will be setup as wired units.. so it works pretty much automatically in the airport utility.. The AE that is going in after the CPE210, still should be configured on a short ethernet plugged into the AE Gen5.. and it should setup in such a way that it is bridged.. and creates a wireless network using the same wireless name and same password as AEgen5.. same on all of them.

It would be better to use a different SSID on the CPE210 to keep it separate as your outdoor link. But the setup of the TP-Link should also be straightforward.. One will act as WAP and the other as client. They should be on the same IP address as the AEgen5.

The thing is that I want to place one of the access points after a radio-link (TP-link CPE210) and have the same network on that accesspoint (same SSID) etc

I'm not clear on whether you want the TP Link devices to use the same SSID as the AirPort 5th Gen and 2 AirPort 4th Gen devices.....or.....whether you want the TP Link devices to use a different SSID than the AirPort network.

Can you clarify on that?

I assume that it is possible to set up the first TP Link device in Bridge Mode....so that it will be on the same subnet as the AirPort network......but I do not have a TP Link device here to test.

Does anyone know if that is possible?

It should be, assuming Bridge Mode capability of the first TP Link access point to allow it to be on the same subnet as the AirPort network.

And how do I set up that accesspoint?

How you set up the "bottom" or "remote" AirPort Extreme will depend on whether the TP Link devices will use the same SSID as the AIrPort network, or the TP Link devices will use a different SSID from the AirPort network.

The distance from the desired location to the Airport Extreme makes it impossible to use a repeater /range extender. Any tricks to doing this / will this work?

It is not impossible to use a range extender. In fact range extender is generally the best method cost wise and ease of installation. You had the right idea with the long range outdoor type units.. The ones made by Ubiquiti are more popular than TP-Link but whatever is in your budget.

Running 100 yards of ethernet outside.. poses some problems. you should either bury the cable in a trench (use some electrical conduit for extra protection) or run it overhead along a fence or along a catenary. There are special grades of ethernet made for outdoor use.. UV protected plastic sheath and shield protection against lightning. Running ethernet long distances outdoors it is especially vulnerable to lightning.. so using properly grounded cable is essential.. as well as using a small switch at each end as a sacrificial device that can help stop spikes by killing a cheap switch before it gets into your expensive routers and computers.

There are alternatives to using ethernet the whole way.. for example powerline adapters are made to suit phone or coax connections as well. I spent some time doing the tests for using cheap powerline adapters over a single wire pair like phone wiring.

Modify powerline (EOP) adapter to phone wiring - LaPastenague

A set of normal AV500 powerline adapters could easily give you 100Mbit duplex over 100 yards with very ordinary phone wire.

Use CAT5e or CAT6 Ethernet cabling. You can run Ethernet cabling up to 100 meters.....(about 108 yards).....with virtually no signal loss at all.

Connect one end of the Ethernet cable to a LAN <--> port on the back of the "main" AirPort Extreme and the other end to the WAN "O" port on the device that will be used as an access point.

If you are going to use another AirPort Extreme or AirPort Express as the wireless access point, the setup is very simple using Apple's AirPort Utility setup "wizard" on a Mac laptop or iPhone / iPad.

If you want step by step instructions, we need to 1) confirm that you will be using another Apple device as the wireless access point and 2) whether you will be using a Mac laptop or an iPhone / iPad to set up the "remote" AirPort device.

If you are planning to use a third party device as the wireless access point, you will need to follow the configuration instructions provided by the manufacturer of the device.

It works because it is plugged into the TP-Link wireless bridge by ethernet and so can create a totally different wireless environment.. but matching the Airport..

It is simple to do.. As already commented.. plug it by short ethernet patch cord into the AEgen5.. do the setup.. then move it to the outbuilding and plug into the TP-Link and it should work just fine.

I am using my Airport Extreme as the wifi hub in my house. I need to add a wireless access point about 100 yards away. I was going to use cat5 or cat6 cable to connect the WAP to the Extreme but dont know how to do this / which settings I need to adjust to allow use of the wireless access point. The distance from the desired location to the Airport Extreme makes it impossible to use a repeater /range extender. Any tricks to doing this / will this work?