AO map isnt really needed, and if you do want to use it, its often better to just multiply it with your albedo map.
As for the texture seam, since its just a regular texture, and not one made specifically for that rock, this will always be the result.
There are workarounds (additional uv-map with different uv-islands that are vertex painted over the seams) but its a lot of work.
You could try using pixexix (http://pixexix.sophiehoulden.com/) but thats only for the albedo/diffuse and needs some cleaning up afterwards. It is a great tool to get rid of basic seams though.
Also, you dont want a regular value in your roughness but an actual roughness texture.