1-Poser has something called a 'shadow cam', i'm not sure exactly on the rules for using it though.
you can look through it to see where a light's shadow will fall,
but something about, you have to render it once first?

2-As far as swapping uvs,  UV Mapper Classic can export .uvs files from V4 and M4. 
I ended up saving two extra .cr2's for M4 and V4.  V4 default, V4 with M4's uvs, M4 default, and M4 with V4's uvs.  iirc, there was a precise tut in the member's only forum with all the steps.

3-after you dress a character, etc, you could save it to the library, figures with the parented props, hair, morphs, etc.  
when doing a complex scene, i like to save the dressed characters to a folder i call Pedestrians for temporary stuff.

you can merge a file, but you end up with extra lights and what-nots.

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