SergioT wrote
Should Omada be able to manage the new EAP225 in the remote link side? So that I can set it to ROOT in the mesh.
Omada controller can manage all EAPs in the network, no matter whether the EAP is in the same network or in a subnetwork. A mesh node becomes a root node by simply wiring it to a router, a switch or a wireless backhaul. No further settings are needed in the controller.
BUT, will ROOT AP still be available to connect end devices, or it is root dedicated?
Depends on your policy. You can either permit clients connecting to the root node or you can deny them to do so.
I read in the user manual that mesh is performed in 5Ghz Radio, Does it mean that Mesh APs will only serve WIFI for endhosts in 2.4Ghz? If so, can we change this behavior, -like switch the radios?
Yes. If you want to disable the 5 GHz band, just don't create a wireless network for 5 GHz. The 5 GHz radio needs to be enabled for the mesh; it uses a hidden network which can't be used by ordinary clients.
For this particular APModel, EAP225 Outdoor, what's the signal strength recommended for mesh links in 5Ghz?
The higher the RSSI, the better. To avoid bottlenecks you should place mesh nodes nearer to their uplink nodes (½ of the max. range of an EAP225-Outdoor, that's 50m). Also make sure there is a free line of sight between the mesh node and its uplink node.
Also keep in mind that a mesh will not increase the total user capacity of the network. If you have one root node and 10 mesh nodes connecting to it, the total user capacity for the whole mesh network remains the same as for one EAP225-Outdoor only (that's ~60 to 80 clients depending on their use pattern). Also, bandwidth of the regular 5 GHz network will be cut for those clients using the 5 GHz band. Additionally, 5 GHz clients can cause the Hidden Node Problem if they are far away from the next hop mesh node.
A mesh is great if you need to connect a few EAPs which can't be wired to the network for whatever reason, but it's not suitable to serve a big audience.