Just a few background questions:
What app did you use to build your house?
Did you draw it in 3d or 2d?
Kadota5.cyc for example seems good to me. Did you build that in cycas or import it?
Kadota2.dxf is wierd because it seems like a 2d floor plan but is actually made of 3d lines all in one plane.
The toilet dxf s as you say will not import. This could be related to dxf version, units or scale factors.
What I usually do is import with intellicad and save as dxf 2000 ascii. Cycas usually accepts this. But not in this case...
Another option is to use a converter like ECadConverter to convert to dxf 2000/2002.
I´ll try a few more things and keep you posted.
If you import any dxf into cycas the 3d objects will be made of triangular surfaces. Hence the diagonal lines. It´s just the nature of older dxf data. More recent dxf versions can contain polygon data.
And also, dimensions and annotations are not 3d data so they will not appear in any of the 3d views in cycas. Although they should appear in plan view.
Text size and dimension size often have to be adjusted when importing dxf s from other sources.
Hope that helps a bit!!
PS I have had success with dxf s from the Kohler website:http://www.us.kohler.com/tech/cadsymbol/readme.jsp