Well, when I think "aliens in Star Wars" I think of a few specific species: Twi'leks, Rodians, Wookiees and maybe a handful of others immediately spring to mind. But when taking Mass Effect as an example, there are a few species that are very prominent (I'm thinking Asari and Turian, maybe Salarian too) and others that feature less heavily (Drell, Elcor, Volus), so there's more room for adding species that we're less likely to see: maybe Chiss, Bith, Zabrak. It also depends upon the context that you're aiming for: like the Sith, while being extremely important in SW history, don't feature that much and are arguably less iconic than even some of SW's lesser species.
Mass Effect is a good model to go by, but they're more physically diverse than SW aliens. Sure, Wookiees and Gamorians are bigger and tougher, but Twi'leks, Zabrak, Chiss and Rodians are only really different aesthetically. I bring this up because I was about to suggest modelling the structure directly to Mass Effect's, loosely assigning each alien a SW counterpart, but I don't think it would work as well. You could still do that though - it's a nice system, because each Mass effect species has their own specific qualities. More difficult to apply to Star Wars, but possible, I think, at a stretch.
Disclaimer: I write this after a... hectic night out and several drinks (more than I intended, but I got home safely
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It's a long road that has no turning - It's never too late to mend.
The darkest hour is before the dawn, and even this war must end.
Pan Galactic Gargle Blaster - Widely considered the galaxy's best drink, the effects of which are like having your brains smashed out by a slice of lemon wrapped around a large gold brick.
~\\*.. The Real McCoy ..*//~