Personally, I wouldn't mix Kunekune with traditional breeds - the GOS will root up all the grass the Kunekune need to graze and their feeding requirements are totally different - so if they were all in together you'd find either your Kunekunes were getting too much (and getting really fat) or your GOS weren't getting enough and not growing as well as they should.
If you could split the paddock with temporary fencing that might work okay, but it's good practice to keep the new pigs completely seperate for
at least a fortnight, just to be sure they're not carrying any diseases that could transfer to your Kunekunes.
We aim for 85Kg live weight for our traditional breed pigs (40 inches when measured round the body, directly behind the front legs) which will give you a carcass weight around 50Kg.
For mixing - uncastrated boars and gilts mixing would be a situation I'd avoid no matter what breed (potential for taint and unexpected arrivals

) but if the boars are castrated it would be alright.......just watch for bullying if you do decide to mix them.
HTH
Karen