From Kochi via NH 966B you reach Munnar Kumily highway via muvattupuzha you reach Thirumangalam pallapatti road, then turning towards Villupuram highway entering Madurai then taking NH 87 reaching Rameshwaram is easy. On the way is Munnar where you might want to take a break or you could plan a break in Madurai. Kindly do check once with the google map too. Yes March April is an ideal time to visit Rameshwaram. With beginning of summer weather will be hot though not scorching.