It's too difficult to figure out what size of your model should be scaled. Only two features I would recommend for your reference, one is for what kind of scene you are working on, the other is for what's the max luminaries' volume amount within your scene. You cant assign only 400 lx for every region lights in a 400mX200mX150M scene, at the same time. you cant assign 4000 lx for a 400cmX200cmX150cm scene. It must be white-out.

The second Q is over the same way just as like the above one. You have to make decision with yourself. The porper meshing subdivision dorminates what the final lighting effect(not the meshing smooth) you can gain. You must make sure what the Max/Min drag slider works for at first. Check your LS's help file for detailed info about that part's describes. There ought to be indicated throughoutly out there.

In case you need further assistance, pls visit our user forum http://support.discreet.com/~Lightscape