1

Is the race of any protagonist subject to any particular achievements, as in "get a Twi'lek to level 50" or so?

All *species* except Cathar and Togruta have a "to level 50" achievement.

For humans, reaching it will give all present and future characters on your legacy a +100 bonus to Presence.

For the others, getting one character to level 50 (by levelling up normally from 1)(1) will remove the class/species restrictions for that species, allowing you to make further characters of that species in any class. When you do this on a Zabrak of either colour, it completely unlocks both colours for all classes.

These achievements can be short-cut by buying species unlocks from the Cartel Market, except for humans.

(1) That is, using an Outlander token or Master's Datacron will not unlock these achievements.