Thinset will work just fine with the greenboard---some like to prime the board first---I never have --and that never caused me trouble---
Forget the liquid nails---way to slow to set---thinner than thinset---and much to messy and expensive----It would work---but more trouble that it's worth---
Forget the liquid nails---way to slow to set---thinner than thinset---and much to messy and expensive----It would work---but more trouble that it's worth---