My question would be whether this patch removes the need to install every previous patch manually(i admit the last time i played and installed witcher 2 is 5 months ago, some things could'be changed)

It would make it far easier on my little brother to install this game once the enhanced patch comes online.

I'm not sure any news has been released yet about how GOG's version will be updated/downloaded, but given that the game will be automatically released as the Enhanced Edition from April 17 onwards, I'd assume you wouldn't have to manually update it much past that (if at all).

Also, I bought the Witcher 2 off GOG back during the winter sales, and I never had to manually update it with a bunch of patches. It automatically downloaded as version 2.0; I only had to manually patch to 2.1 -- and, arguably, that patch doesn't even really affect gameplay anyway.