My opinion on your queries are as under:
1. for how may period, i will pay interim relief
Opinion: Till her life time, or if she is working and able to maintain herself, or till her remarriage after getting divorce from you, or till the appellate court set-aside the order.
2. can i appeal again for decree of divorce, if yes in which court
Opinion: yes, you may file an appeal before SC against the High Court Order.
3. we are living seperate for last 24 years, can i remarried from other women without getting divorce.
Opinion: Legally Not, it is an offence as per section 494 of IPC as Bigamy.
4. if not remarry, can i live with someone as "live-in-relation" or as "naata" to some one.
Opinion: legally Not, it is also an offence u/s 497 of IPC as Adultery.