GST on Lodge Rooms

I am having a lodge with multiple room rates, but less than Rs.1000.00. At present my turnover is less than Rs. 20 Lakhs. Now I want to increase my room rates. So I want to know:-
1. Should I take GST registration even before making Rs.20 Lakhs turnover.
2. If so, should I collect GST on every rates or rates exceeding RS.1000.00 only.
3. Whether I am eligible for Rs.20 Lakhs exemption even though my room rates are between RS.500.00 to RS.1800.00