You actually don't need to complete all side quests and bonuses to keep up to level with your class quests. Not even close, actually, especially if you do FPs, Heroics, Space battles, or PvP.
That being said, more content is always good. It is also expensive to develop and I'd much prefer that time and money be spent on endgame content at this point.
When I first hit 50, I used planet commendations (of which I had many saved) and ran low level FPs solo to get orange moddable items and then crafted the appropriate mods.
I bet you won't. In thousands of items, I have never seen a crit on any enhancement, mod, barrel, hilt, color crystal, grenade, etc. I have only seen crits on fixed-stat slot items such as (non-orange) armor or weapons.
What is the difference between watching your companion's progress bar or your own progress bar other than with the latter, you can still do other stuff too?