There's certainly no problem with getting in close, I often use a full set of tubes/bellows with my 100mm macro lens attached.
Also remember photostacking is not just for macro, as you can also use it on landscape.
http://www.worldphotographyforum.com...999&ppuser=150
http://www.worldphotographyforum.com...066&ppuser=150
http://www.worldphotographyforum.com...at=&ppuser=150