With any Bryce, be it PLE or Pro, you can import/export as .obj, 3ds, Lightwave files and objects, and a few others, check file/import objects. The problem is with the materials, not all imports will bring the materials with it, and if importing an object with multiple textures, they will all seperate, and is difficult to put back together, and some you will be able to ungroup and texture yourself on imports. But you can export as an Object Bryce Preset, or a .obp to use in bryce. 

As to the final size, the only restrictions I have found were within Bryce, in the internal memory, Bryce being only a 24 bit program, if you cram too much into a scene, you can easily run out of memory. But I haven't really made any ginormous renders, so not sure.

Hope this helps. 

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