I am not sure where you are on your trip – posting as you go or posting after the fact – but my family and I live in Antananarivo and I have ridden the whole west coast from Mahajanga to Tulear.
Weekend rides are north and east of ‘Tana.
Paulo and the guys at Motostore were reasonable in recommending that you be cautious in the south. It is remote and a little troubled, but beautiful. PM me and let me know when you are back in Tana. We are about 5 minutes from the Motostore.