Hi,
1. LTE sample is represented on 4 bytes, in CPRI: 15-bit I, 15-bit Q
2. This is up to the application, the push/pop of the LTE symbol packets could be at symbol rate, slot rate, or even subframe rate.
3. Once started, the application needs to continuously provide Tx packets not to starve AIF2 PE. If you need to send 0 data for some reason (application crash for instance), you'd need to disable the PE channels.
Best rgds/Seb.