Implementing EHP 4 and 5

Hi,

Currently we are running ERP 6.0 with EHP 3. I am asked to study EHP4.0 and EHP 5. It is my first time working with EHP.

Is it possible to implement some parts of both enhancement package or we can implement the only one?

Is there any tip for assessment the EHP, which one is better for our organisation?

I read in one of thread, that EHP 5 is only for Ramp-up customers. What does it mean? How can I know, whether we belong to Ramp-Up customer?

Thanks