Best time to visit Meghalaya is September - December. This time, the waterfalls are in good volume and are very beautiful to look at. It is a really good and safe place to explore, so go ahead without any hesitation.
Yes Meenakashi it is safe.I visited there in April 2018.Threre is a government tourism office in Shillong from where daily buses on share basis go to all points in Meghalaya.Bus will drop you back to shillong after every evening.It will take you 4-5 days to cover all points.. You can ask any query related to above.
The ideal month I would say is November. Though the ideal duration is September to Mid January.
Try spend 2 days in shillong and 3 days in cherrapunjee. There are other places for trekking in meghalaya.
Safety point of View- The place is safe and people are welcoming..
I would suggest you to check out my blog for the same.