Reached lvl16 with my Sith Inquisitor. While annoying, the restrictions aren't too bad. That is if you really just treat this as a solo/co-op game and mostly play the story. You only have to buy stuff or need to sub, if you want to play Flashpoints and Operations often, or get into Endgame stuff and PVP.
What I'm doing right now, is I'm playing the Sith Inquisitor story, wait till most of the bugs are ironed out, because there are a ton of them, after they implemented the F2P system, like Cartel Coins not being awarded or subscribers being treated as F2Pers. Then I'll sub once, collected my Cartel Coins, buy unlocks so I have access to all quickbars, crew skills and other basic gameplay elements, so I can enjoy the game fully, even if I don't sub. And whenever I'm in the mood to PVP heavily and do a lot of Endgame stuff, I'll occasionally sub for a month. Then once I've got it out of my system again, I just focus on the story.