The rulebook hasn't changed
Yes they can be used together by allying together.
A noteworthy change to the game is the warband system, which means that a hero/captain has to lead up to 12 guys.
i.e. I take Faramir who lead 12 warriors of minas tirith.
This also means that if you have a Mordor list but wanted some Isengaurd Uruk-hai you could only do this by taking a Isengaurd captain/hero and then take up to 12 guys.
On the points, I have no idea. I play occasionally with my friend and we play 500 points but you can any points
tbh (One of the special scenarios in the Mordor sourcebook allows for 1,750 points of Mordor

)
If you get a sourcebook everything is explained much clearer than how I explained to get one!
Hope this rushed answer has helped a little.
Happy Playing