Very difficult if you are learning C++.
Theres no point implementing it anyway. UE4 takes care of this for you using world composition.
Its unreasonable to have 1 large landscape in one large cell. The further away from 0,0,0 you are the less accurate everything becomes, causing all sorts of problems.
Using tiled worlds you can essentially have an infinite landscape so long as your computer can handle importing it. You get the same thing as having one large landscape peice, except it doesnt kill any pc trying to load it as its split into sections that stream in automatically as you walk around.
@ gregsandor, read my post here about world machine to UE4 landscape scaling
Also, your heightmap should be 4033, not 4096.