out of curiosity, why are you straying so far from the standard bodybuilder 4-6 day split?
I do like the idea of hitting a more full body workout, then doing cardio afterward as I believe that maximizes fat burning as you are depleting the most glycogen in that case... but your volume may not be enough to completely sap your stores. One exercise for each major bodypart doesn't seem enough.
What I would do is try to follow an extended bodybuilder split where you do a large muscle group, and 1-2 small muscle groups each workout session, ie chest biceps abs. And continue until you finsih your whole body. A 30-45 min cardio session after these would be fine.
then on your HARD cardio days, you can do the above mentioned full body workout with more volume, then follow that up with a nice low intensity burn of 45-60 minutes.
the standard bodybuilding split will do wonders for "retaining" your muscle mass as you will get a better pump and keep signaling the muscles that they need to maintain (or if you're lucky) increase their size. The full body workout will not do much in that regard especially for a trained individual.