Hi tarpon
1. Try going to the drop down window "3d view" and select "display all levels".

2 by merge i am going to assume you mean to show all furniture (objects) on 1 level instead of 2 or 3, if that is the case, select 2 or 3 items on the level to move, then right click >select all, you can then either cut and paste to the required level or copy/paste whichever you are comfortable with.
Mike