I assume you have, or at least know of, the two volumes of Mann/Fux (The Study of Counterpoint and The Study of Fugue). If not, they are a recommended read.
There are a number of contrapuntal devices that you have left out of your repertoire. This is, of course, fine - in that no one work (at least a short 2 part invention) should try and cram too many in.
You have been pretty conservative harmonically (and melodically too).
Not suggesting you start on a fugue (yet).