Hello,
I have seen around 3000 GUPs configured in single liveupdate policy as multiple GUPs and they are working fine.
Clients will find the GUP in its subnet.
If you want you can create explicit GUPs if you have thr requirement or as backup GUPs , however multiple GUPs will work fine and clients will know which GUP to pick up,it just should have the policy applied.
In reference to the Liveupdate policies, you can apply only 1 Liveupdate policy to an client associated to a location.
Hope that helps!!