Igor - the first thing to say is thank you for your efforts in thinking how best to set this up and your proposals : )
However - for me the whole thing is too complex and too rigid. Personally I'd just have one forum. However I would make it essential that the original poster tags the post to make it searchable. Maybe you could set up tags for 'Home DCC' - eg: I'm doing this in 'C4D' and 'Target DCC(s) eg; I'm interested in how to do this in 'Blender' or 'Houdini' or 'Any'. And tags of course for the 'Topic area'
I think having all the subforums just makes it too complex, too hard work for moderators and too hard to discover for occasional users.
It also makes it difficult when a topic area falls outside of easily identifiable categories. For example, one area I would like to discuss is C4D 'Takes' - ie, does Blender or Houdini have something eqivalent to that functionality? Where would that go? It wouldn't fit anywhere and would therefore be easily lost.
As Dast suggests - I'd also drop any idea of a specific number of DCC's - there's lots of related tools and techniques that might come into play. For example a modelling request might best be solved with something like Zbrush, or MOI3d or something else that is not necessarily a full blown DCC.
So, in summary: I'd keep it simple. Very simple.