like nerdy already said, the swingarm pivot / output sprocket relative position limit how much you can raise the bike.
more than 1.5"-2" and the top run of the chain will be rubbing the swingarm,
so assuming you wan tot keep the stance balanced and not ride a chopper in the dirt, the front cant be raised above 2" either.
this kind of increase in fork length is not going to introduce much bigger forces.
essentially you will end up with a scrambler stance, which should look nice actually, just dont expect to get more than 5" wheel travel for big air jumps.
search for "mcdeeb z400" to see some nice examples of such scramblers
thekneeslider.com/kawasaki-z400-scramble...ic-farm-motorcycles/