Hello,
You can explore the east part and south on 21 days, Andasibe is one of best place to spot the largest lemur called “Indri Indri “ with others diurnal species , if you want to have nocturnal visit I’m sure you will find the tiniest lemur and the diversity of frog, chameleon, after here continue to Ankanin’ny Nofy , you have to catch the boat on Pangalane channel stream up to Palmarium reserve , it has several species of lemur including Coquerel’Sifaka and tame black and white ruffed lemur , there are too a good selection of reptiles, this site offers you a perfect place for relaxation with its beautiful beaches then after here extend your tour to the south follow the National road 7, this tour has beautiful landscape and rich for the culture and wildlife , you can start to visit Ranomafana where you will find “golden bamboo lemur “ one of will be extinct and others species too, best place for the birds-watchers, and then continue to Isalo , stop-over at Anja reserve where you will find the ring tailed lemur and visit Bara ethnic tomb and then continue to Jurassic limestone park of Isalo, you could find the ring tailed lemur too and have bath at natural swimming pool, after the long journey why not relax at Ifaty or Anakao beach , it ‘s in south of Toliara.
Andasibe is in east part of Madagascar that’s means wet area but I think the rain season will be finished on April so you don’t need worry about it.
About Berenty and Fort Dauphin I want not to recommend you because the lemur in Berenty reserve is not wild one and it’s expensive to book this tour with Dauphin hotel in Fort Dauphin but you can decide if you want.
That depend for you if you want fly back to Tana or drive back, don’t forget the flight ticket will cost Euro 150/person for single so for me if you stay few day in Toliara beach why not drive back with your driver.
Good luck!!!!!
Anne