Regarding LMS configuration Guide, i plan to run RME and Campus only on second server for my 5000 devices. First server will be use only as MAster server

That's fine to do, but it's a bit of an overkill. Common Services by itself doesn't require much in the way of resources. It's only when you starting installing the applications does the memory and CPU requirements go up. If you are not dividing your network across these two servers, then you do not have a supported configuration. RME and Campus only support 5,000 devices each. Even if you had a firm 5,000, you would also not leave yourself any room to grow.

What you say is that RME supports 5000 devices maximum ? Is there a technical reference for this point ?

Same thing for Campus ? What should be the best design for you in our context (5000 devices to manage)

Correct. RME and Campus currently support 5,000 devices max. This is documented in the installation guide for both as well as in the LMS bundle documentation.

I recommend you leave yourself room to grow, so if possible split the 5,000 across two servers. This will, however, require two different licenses since you will need to install a copy of RME and Campus on both servers.

I already have two different license, one for master and one for slave. Isn't it ?

Common Services is unlicensed, so in your initial design, you would have only required one license. However, if you did get two licenses already, you will be okay to spread your network across the two servers with RME and Campus on both.