The more the better for tx propagation and block validation. I think 5000 is good enough, if it grows with the number of txs, not reduces.
the more nodes = delay in propagation. because it takes time between each node getting data to check it and move it on.
but
the more nodes = more copies of the blockchain. so if something bad happens in one locality there are many copies in other localities that no one cares what happens in small area's
more nodes is not about propogation efficiency but about diversity and reducing risk of targetting limited numbers of data holders