/3/ - 3DCG

>>591338
Low poly is a relative term, as it can be anything that's suitable for use in real-time applications or for animation. How low is enough for you depends on what you're doing with it.
High-poly generally refers to any subdivision surface or multi-million poly sculpt, anything that for all intents and purposes isn't usable outside of production rendering or for baking down to a low-poly.

>>591347
What program you using? In Max you can draw a spline around the intersection of the two objects, enable it as a mesh, turbosmooth it, add a displace modifier with a cellular noise map, and then smooth it again.