One thing to note, for each object in max that you have, it would make a new draw call in the engine.  [...]  I once used that a lot for draw order in 3impact for my race track environments.

now that you say that, it have all the sense in the world!!

if I model transparent things and create them in certain order in 3dsmax, save the whole thing as an single .x file and use it in a single skinmesh object in 3drad, that allow me to trick the infamous trasparency problem (props to shadmar's vegetation shader!).

however  I've just tested this: some transparent models in 3dsmax, merged them all in the same mesh and save it. I tested 2: one all merged in a single mesh, and another all the separete objects. as before, in mview the one that I merged all in the same mesh have a more than 10X better framerate.

this time I looked for that hierarchy you mention, the merged one dont have much hierarchy at all, just one object. the one I exported all the separete objects have a hierarchy showing all the objects.

so far, that seems perfectly normal.

what really caught my attention is that I thought that the draw order enginered through modeling order to trick the infamous trasparency would be affected merging everything in a single object, my bet was I would be able to see the first object only. surprise is the draworder remains intact, with the same object.

so, according to mview hierarchy I have just one object, but 3drad draw everything in the intended order... so, how many drawcalls are being made despite the amount of objects?

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what a mess I just wrote! 

This is a great discussion to have in mind regarding map building.   Logically,  3drad lends itself to the idea of being a powerful level editing tool.  But taking into these considerations (not to mention the object limit)  one would think you could get better results by exporting your map as a single model mesh into 3drad. 

Or am i not understanding this correctly?

So if you use a single model with different textures: what is the most optimised way to use it in 3drad? Is it by splitting up the model by texture and use different skinmeshes for each one of them, or to export it just like a single model?
What is the maximum number of textures per model?

So if you use a single model with different textures: what is the most optimised way to use it in 3drad? Is it by splitting up the model by texture and use different skinmeshes for each one of them, or to export it just like a single model?
What is the maximum number of textures per model?

There is no maximum for the number of textures you can use in a .x file, but there is a limit in the max textures that can be allocated by 3D Rad (adjustable by modifying the arrays.ini file in the main 3D Rad folder).

When using multiple textures for a single SkinMesh, it all depends on how exactly the .x file exporter you use arranges the different geometries in the .x file.

Usually there will only be one single piece of geometry for each texture, but in some cases (sometimes depending on how exactly you have designed the object in the modeler) a group of polygons that share the same texture may be split into different 'geometry pieces', causing unnecessary overhead.