Is it even possible to complete the Codex? With several planets being restricted to the opposite faction it would be impossible to collect the Codex entries for those planets.

Also I am assuming you have to at some point travel to the other starting planet to pick up the Codex entries and Datacrons for that planet? (ie. Sith traveling to Hutta) Is this the case?

I'm pretty sure there are alternative ways to obtain some codex entries. The reason I believe this is that many entries are submitted for multiple planets. For example, the Manka Cat entry goes towards Alderaan and Tython.

Also, the Codex is dynamic. As a Jedi Knight, only 4 Lore Entries are needed for 100%, whereas a Jedi Consular needs 5 Lore Entries as they obtain one automatically in one of their quests that Jedi Knight's cannot obtain.

THIS OF COURSE IS NOT CONFIRMED, I AM MERELY SPECULATING.