Release : 10.7.0
Component : APM Agents
1- SP2 agent can report to APM 10.7 SP3 Enterprise Manager.
2- No, you will not lose historical data for SP2 agent, but it is good practice to make a back up of historical data before upgrade.
3- Yes, you can have both SP3 and SP2 agents installed on the same Linux server. SP3 and SP2 agents must be installed under separate location, and must monitor different Application Servers (meaning one Application Server can only be monitored by one agent).