Welcome to our Mogre world.
First of all is to say that it needs very much time to create games. So maybe it's good to keep the personal requirements simple. Then you have a better chance to finish your game. I don't want to hit you. It's just common experience.
Myrddin [...] is not compatible with the current Ogre/Mogre version
If I remember right, Myrddin or an other user could update it for usage with Mogre 1.7. (many months ago) But I'm not shure. Look through the ~20 latest posts of the forum topic.
It's a great looking SceneManager, but I suppose that only less people do/did use it. The developer want's to improve it, but has no time for it for 1 or 2 years now. Sometimes he gives answers, but not much more.
Also be aware that there are not many people who can help, when you have problems with it, because of the less users.
On the other hand - if you can get it run, you can enjoy the sweet terrain.
It's your favorite. So just try to compile/update it your own. Give yourself a limit. (e.g. one week of testing) For problems/questions ask in the Myrddin forum topic. If nobody helps, then skip it.
If you import terrain as mesh, then it's not so performant as terrain managers, but then I suppose you can use each SceneManager as you want.
I just have experience with the Terrain Scene Manager.
For my application it's well.
In Ogre 1.8 it was removed. We want to try a trick to keep it also for Mogre 1.8.
If you stay with Mogre 1.7 (still pretty well), you can use it out of the box.
Terrain and paging component:
I suppose somewhere in the main
forum are topics with code snippets. You need to search for related posts. If you find nothing, open a new topic in the main forum. There are much more users and you have better chances for related answers. The usage with Mogre should be similar to Ogre (C++). So don't be aware to read and ask additionaly in the Main forums.
The terrain component is for one big terrain. When you use it in combination with the paging component, you can split it to several terrain chunks. This is what I understood by reading terrain topics.
Many months ago I read, that the paging component has no good speed optimization. I don't know it somebody improved it now.
This year was a GoogleSummerOfCode project. Either to terrain or to paging. I don't remember.
Be aware that our Mogre wrappers for the new terrain and paging component are only alpha versions. We don't know how stable they are or how much was wrapped / is missing.
I don't know much about paging.
Mabe you always see all chunks in your direction of view. Perhaps only the terrain of the backside of the camera will not processed. Well, just an idea. I don't know if my assumption is right.
As I said: Look to the Ogre main forums. If you don't find what you want, don't be afraid to ask there.
In most worst case (when you really need paged terrain), you should consider to use Ogre (C++) instead. Then you don't have problems with the lack of a stable terrain/paging wrapper.