Well I've been forcing myself to do the f2p method just to see if it can be done. (and thanks to christmas, no money for a sub )

Currently have a level 23 marauder and a level 11 assassin, and a level 2 legacy.

The speeder at level 25 can be negated with the legacy perk, as can some of the xp penalty (f2ps and preferred get 25% less xp then subs for those who don't know).

Biggest issues I'm having are the 200k credit cap, the one crew skill slot, and the 3 loot rolls per week for flashpoints though you can get the passes/unlocks off the GTN if you can find some listed within your credit cap, and the xp boosts are fairly cheap (3-5k each for the minor on the server I'm on).

All in all, taking into account legacy and being able to grind credits for the cartel stuff off the gtn, the f2p isn't bad, just grindy, and end game seems to be near non existent for anything but subs (obviously).