Should I open SRS Account, knowing that my income tax is around $70 with a tax rebate 50% which is around $33?

Just some simple answers based on the lack of information in your question!

No, because you're only paying $70 in taxes it's not worth it.

But yes, using $1 if you're expecting your salary to increase beyond $80k annually in future, because the withdrawal age is locked based on when you open the account.

Based on last week's news, the government is reviewing and may increase the withdrawal age in September.

It depends. No one can provide you with a clear answer without knowing what you want to use your SRS for. But if I was in your shoe, I wouldn't do it. The tax savings does not justify the inflexibilty caused by contributing to your SRS. Also, how much do you need to contribute to your SRS to lower your income bracket? If the amount is only a few thousand dollars, it is slightly meaningless as once again you are limiting yourself to a few investment strategies which are usually lump-sum based.