So u can unlock items and gear trough legacy that helps u out when u make a new char, and basicly makes ur lvl 10 companion 3 times stronger then u? What level of legacy would u need for that?
As mentioned above, the human race legacy unlock gives all your characters +100 presence. This is a sorta nice bonus if you're high level, and a huge difference when you are starting - a level 10 typically has about 40 presence, so you go to 140. Maybe "3 times stronger than you" is a bit of an exaggeration, but it certainly is a noticeable difference.
You can unlock it either leveling a human character to 50, or with 500.000 credits. It has a minimum legacy level requirement, not sure of the exact value; and I believe you can also buy it with Cartel Coins. You can check price an level requirement in the Legacy window (Y key if you have not changed it), species pane.