@Venkatesh, the number of managing nodes will depend almost entirely on your license and the "Nodes" count within it.
There is also a "tiered" managing node approach which is commonly used in highly segmented environments as well as large scale deployments that have thousands of nodes.
In larger deployments, say greater than a couple hundred nodes, the use of "Entire Network" is not too practical (especially in IRGUI) and at that point its best practice to utilize custom defined node groups.
The configuration can then use route-to statements as well so each level of managing node only needs to "managing" a subset of monitoring nodes and then that information still gets fully available further up the tiers.
If you are not already planning on attending IR Summit, I would suggest you do as we will actually be having a session specifically on "Large Scale Deployments" as well as several other good sessions that I think you would find of value.
Christopher
