I think your level deficiency might be a result of you skipping quests. AFAIK, the XP nerf doesn't kick-in until level 10. (That's how it was on the PTS.) So it shouldn't even be a problem yet.
But even if they did change it, it shouldn't be noticeable that early in the game as long as you do all the quests. Be sure you always get the bonus objective(s) also.
As far as taking on a level 9, the only thing I can think of is you wondered off to someplace you didn't belong. Stick to the rails. They're a total pain, but they keep you were you're supposed to be.
The only other thing I can think of is there is, if you're on Tython, there's a level nine elite in the level 4-6 area. You might have run into him.
Honestly though, I think people are making a big deal out of the F2P Xp nerf. As it is, this game hands out Xp like candy, and it's really easy to always be over-leveled for whatever planet you're on. I suspect, with the nerf, you'll just be closer to the normal level range. Apparently, they give the Xp boost items for quest rewards too.
All in all, I really wouldn't worry about it.
And I don't know what you mean about the gear costs. Quest gear and planet com gear is the same either way and twinking is completely unnecessary in this game. You should never buy any gear with your first character ever. Save your credits for skills (They start to get REALLY expensive 35+.) and on crafting should you choose to do it.