Blender's internal renderer is much more efficient than Poser's.  and most renderers Blender works with are more efficient than the Blender internal renderer.

most of the Blender images, Indigo images, and LuxRender images have been about an order of magnitude more complex than just about any Poser image i've seen.  to be honest, large scenes are a Poser weakness, not strength, and i've never heard of a renderer that doesn't out perform Poser in that respect, including D|S.  maybe you could give some examples of what Poser could do that another app couldn't?

will you have to learn a whole new way to work with materials if you switch renderers?  yes.  afaik, that's true if you go from Blender internal to Indigo, even if you use Blender to set up the scene for both.  just start small and build your knowledge step by step.

i think the big issue is material zone count.  because Poser itself is less efficient (can't create multiples, for instance), and because the Poser community has a lot of inefficient habits like extra material zones that hardly anyone uses, Poser models often have a lot of material zones.  iirc, Blender 2.49 and lower (i'm not sure about 2.5) only allows 12 material zones per object.  so you might lose some zones going from Poser to Blender.  that said, i've only used V4 (for instance) as a mannequin, and i've seen lots of zones on her, so maybe it's not a problem.

some words of advice with the cameras and the scene:

• center your focus (main figure, main object, etc).
• when importing things to Blender, scale up by 10 (it's easy to remember, and neither too big nor too small to work with)
• in Blender, put your cursor at the focus.  if its center point is at 0, 0, 0, that's easier to do.
• when you select and transform your rendering camera, use local co-ordinates and rotate about the cursor.  that way translating along local z will allow you to zoom, and rotating will keep your subject in the frame.
• before rendering, make sure your camera is at aperture for your distance.  for instance, you want something larger than 35mm for  a close up, and lower than 35 mm for a really wide angle.  
• give your rendering size the appropriate ratio for your scene.  for instance, don't use 600 x 800 for a wide, panoramic scene.  try something more like 800 x 400.