@Giorgos20cy 

Honestly.. ditch the EAP115 walls and either go for full EAP225 APs or 6xAPs

The 1x range is really old now and lacks a lot of features (roaming for example), therefore it will limit you massively and likely wont be supported much longer.   Also the Wall editions dont have as good a range / signal vs the standard ceiling versions due to the fact its crammed into a wall slot.   Go for a 2x range standard AP, or a 6x if you can stretch the budget.    Most people go for the 225

If you are after seamless roaming then stay away from the wall editions, they generally dont have it (except very latest 6x versions), this is by design as they are for a single room / hotel room where roaming isnt needed.   The good old fashioned EAP225 Ceiling/wall mounted is the most common choice and supports roaming or go for a 6x AP if you have the budget.

  @Philbert 

Thank you for your response!

Ok change of plans.

So, if I go for:

• TP-LINK ER605 V2 Omada Gigabit VPN Router

• TP-LINK TL-SG2008P V3 8-Port Gigabit Smart Switch with 4-Port PoE+

• 2x TP-LINK EAP225 V4 AC1350 Wireless Gigabit Ceiling Mount Access Point

Are all compatible with each other for seamless roaming? And, do I really need the router or I can connect everything to the SG2008P and control everything from the Cloud Controller?

  @Giorgos20cy with the assumption this local network will have internet access,  and you will have an ISP provided router,  I don't think the ER605 is necessary unless there are features it offers that you need, which the router the ISP provides may not offer.

  @Giorgos20cy 

Hey again, no worries happy to help!

Suppose you go for that setup, yes its compatible with seamless roaming.   APs that can handle seamless are the EAP2xx range and the EAP6xx range, as mentioned earlier however the wall variations are the exception due them being designed specifically not to roam.  Note some of the vvv new EAP6yy wall editions are starting to come with roaming, but it's literally one model.

So in answer to your question about a router..   Depends on what you want to achieve ultimately.  

• Should you just want managed WiFi with seamless roaming, Mesh and some controls over clients, then you DONT need the router.  
• Should you want VLANs, Bandwidth control on the WAN and VPN then YES buy the router.

Those are the main selling points, up to you how you wish to do this, personally, I ran without the router for 6 months or so with the same hardware you are considering.  Remember you can add the router at a later date if you decide you want more control.

In terms of the cloud controller, just ensure you have adequate WAN capacity for this, personally I haven't used the cloud controller as most of my installations go for the OC200 on site (its cheap).  However one client did choose it, he had a limited 40 down / 8 up pipe that was running full capacity 8 hours a day and the cloud controller wasn't the best choice.  When the WAN maxed out he lost management and that caused issues.   In short make sure you have some free WAN capacity for this, you don't need a lot (perhaps 2-4mbps at a guess). 

  @Philbert 

Your explanation to   @Giorgos20cy suits my doubts as well, thank you very much.

In my case I do have an ISP provided router (with wi-fi) but, as I intend to set up 3 VPNs with corresponding wi-fi, and still want wi-fi roaming, I'll have to buy a suitable router, like the TP-LINK ER605 V2 Omada Gigabit VPN Router.

I'll have to find out how to switch off the ISPs wi-fi to avoid confusion, I guess.

From a YouTube tutorial I saw, the OC200 seems quite easy to setup for what I should need.

Best