Sextus Pompey is in no position to challenge Caesar. Following Munda he was just fighting to stay alive. Caesar IIRC had in any case pardoned him, and then he was given legitimate authority by the Liberatore government. It is from there that he was able to build up a power base of any sort. If Caesar is still alive, Pompey is going to be a virtual non-factor for the most part.Sextus Pompey, for one. And he would be no easy man to kill.
As for what Caesar planned to do, first on his list was invade Dacia. This was actually a pet project of his that goes back to his consulship. Before he was suddenly granted Transalpine Gaul, he had secured a pro-consulship over Ciscalpine Gaul and Illyria, with the intention of taking on Dacia and Burebista. I'm not sure if this would be easier or more difficult than his time in Gaul. On the one hand, Dacia is a far more centralized and tough opponent, as opposed to the various quarrelling tribes in Gaul that only posed an existential threat to Roman control there when they banded together. On the other hand, this might also work to his advantaged. Rather than managing a political minefield like in Gaul, he's battling one centralized state. He'd probably win in the end, but it will be a long and protracted campaign.
Following this he planned to take on the Parthians and avenge the loss of the Eagle standards by Crassus at Carrhae. His strategy was probably roughly similar to that used by Antony when he took on the Parthians. That is, march through Armenia, attempt to win an alliance with the Media-Atropatene King Artavasdes, and cripple Parthian power. Unlike Antony, he'd probably manage it much better, both diplomatically and militarily (like not getting his baggage train obliterated). The end goal was probably something along the lines of nominal client kingdoms in Mesopotamia, Babylonia, and Media to protect Rome's eastern frontier.