building objects from parts

I'm new to Inkscape and I can see it is a really powerful tool but I am having some difficulty drawing the parts for a laser cut box.
The bottom and sides are large rectangles with tabs at the edges. There are also partitions within the box which interface with the bottom and sides meaning that there need to be slots in those parts.
So my method for building the components may not be what a more experienced user would use.
I made the partitions by creating a large rectangle and then adding the tabs as separate parts. I've grouped the tabs with the basic rectangle but when I look at outline view I still see them as distinct and I don't know if this means they will be treated as one item by the laser cutter. I duplicated this object and used the Union tool but in outline view the tabs still look as though they are separate although the info bar says 92 nodes which I take to mean this is indeed one component.

I haven't yet looked at the slots in the bottom and sides but I constructed these in much the same way as the partitions using tabs to join multiple rectangles together.

My question is how do I determine that I have created an object that will cut as intended rather than as each of the parts that went into it?