How to publish thesis as a book after getting most of the thesis published as research articles in SCI journals. Do I need to get permission from the journals for copyright transfer before publishing the thesis as a book?
This depends on the copyright license or transfer you signed with the journals. These range all over the place: they may own copyright, you may own copyright, or somewhere in between. If you transferred copyright to the publishers and they did not grant back any rights, you cannot republish without their permission. (Moral for the future: DON'T TRANSFER COPYRIGHT if it is avoidable, which it often is.)
I suspect you will also have to spin this very carefully (and honestly) with book publishers; many will not want reconstituted journal articles.