Say I want to buy something from Amazon US after 1st April, do I have to pay gst beside the normal import duties? Does order from oversea have to pay gst?

Import tax will be imposed if the value exceeds RM500, and how does gst work? Do you have any prove to back up this claim?

Since import duty and sales tax will be imposed when value declaration is over RM500 currently, does it mean this also works on gst too? As long as your parcel from oversea doesn't tax by import duty and you don't have to pay gst as well?

As far as I know shipping cost will be calculated, they will use the total cost(product cost + shipping) as the final price of whether the package will be taxed or not.

I'm not sure what you mean by company being taxed another round, all the custom taxes that I paid so far were for personal use, I only know custom here will use the final price(product price+shipping) as reference for taxing purpose.