question about composite glyphs

I'm using TypeTool Version 3.0 for Mac, and am creating a TrueType font for use in music notation software (Sibelius). The font consists primarily of circles, dots and arrows arranged in various configurations. I first created basic glyphs of the circle, dot and arrow, and then used them to create composite glyphs for the various configurations. I thought this would make it easy to change the line width or dot size of the entire font by only needing to revise the basic glyphs.

I'm running into problems, though. The components overlap in some of the composite glyphs. And in some composite glyphs I've added a contour that overlaps with one or two components. Not all of these overlaps cause problems, but some of them result in the overlap area displaying as white rather than black.

I can get around the overlap problem by decomposing all glyphs and then merging contours. But I wonder if I'm just not understanding something, which if corrected, would make that unnecessary.

Is it allowable in TrueType fonts to have components of composite glyphs overlap?

Is it allowable to have contours and components overlap?

Is there a rule to follow that would make the overlaps not cause white areas?

Many thanks for any help.

Dave Hollinden