Booking new apartment during pre-Launch

APARTMENT IN EMPRASA SMART CITY builder Artha properties and marketed by sqaure yards. I booked an apartment during pre-Launch for 25000 , post which i received confirmation on booked flat As part of the booking they are asking 100000 to block the apartment . post which legal document will be shared . The builder confesses the project approval is still pending . The marketing company says no emi till possession but from the sources i hear its only for 3 years the emi is paid by company building. What are the questions i need to ask them in mail before proceeding ? is the mail conversation considered valid by court in case of dispute? and what are the document needed to proceed further? all the conversation till now is in with square yard , i got a mail asking the balance to be paid in name of hoskote neo homes limited in cheque / online transfer post which agreement and legal process would begin. Have absolutely no info on exact location / current status / pending approval /when project will be launched/construction specification/exit clause , in fact no clear info on anything .