Getting plasterboard flush on studwall

[nitro23456]

We've got a studwall between the living room and dining room with a double doorway in between.

There isnt actually a door or a doorframe so just an opening in the wall in an otherwise standard studwall.

We wish to build additional studwork into this opening to separate the rooms.

I have not done this before but am a fairly able DIYer and the studwork should be fairly easy. My question is how to best line up the plasterboard with the existing wall to achieve a neat finish so that it looks like it was always like that?

Will taping etc work or will i need to get the whole thing skimmed new and old?

 

[PrenticeBoyofDerry]

I would bring the plasterborad walls, flush to the existing.
Tape up joints and skim the entire walls.