Quote - In your experience does Poser work better with absolute paths or relative paths?

It depends on how likely you are to want to move content around (you should also consider what will happen when you change machines) but absolute paths are going to be troublesome at some point.

Quote - Also, is there a way to remove recently used textures from the drop down list in Materials Room other than closing and restarting Poser?

No.

Quote - And is there a script that will open a texture for a selected material in Poser with its default app... say irfanview so I don't have to navigate there to have a look at or edit the image file?

Should be possible.