I am J1 visa holder (with Hong Kong residency, which is not included in the tax treaty).
My salary is only 6000 per year.
I am currently paying both state and federal taxes.

Do I qualify for a tax refund, since I earn so little?
Would I able to get all my taxes refund or just partial?
Do I fill in the tax refund form after the tax year?
Or can I stop the automatic tax withdrawals immediately?

I heard that some J visa holders can apply for rental tax deduction?
Is that possible in my status?

You will file nonresident tax return. On federal return your exemption is $3,400 plus state income tax deduction. So you have about $2,500 of taxable income. Your tax is about $250.

You must file your tax return since your income is over $3,400.