Please find my response to your queries
1. which JDeveloper version should i use? can i use 12c ?
You should use jdev 184.108.40.206 , its pretty stable and compatible with EBS 12.2.7
2. How session will be maintained into ADF?
There is patch provided by oracle for ADF EBS session management, you can refer below link
3. How to call go back OAF page from ADF?
Never tried this though , but what i feel if u able to manage session then through task flow you can call OAF page , i've not done this particular requirement , give a try
You can follow below link for sample ADF migration to EBS