I never get why people on their first character want to get to 55 as fast as possible. A big part of the game is its story (and not just the class story) Why would you want to skip half of the game just to get to 55 quickly.
If you do the class quests, main story line and sidequests of every planet, bonus series and heroics you get to 55 fast enough and you can enjoy the game.
Becuase at 55 the game gets kinda repetitive and boring ( you do dailys, fps, ops, pvp) and they don't get that more interesting the 10th time you do them, so enjoy the story while getting to 55.
As for your legacy perks, buy the stuff that is actually usefull at 55, crafting crit chance, companions affection gains, rocket boots, 1hour travel to starship, bigger inventory...