Technically, under Legends "canon" there are only a
dozen or so species (see the "History" section of that link) on Tython/in the Tython system (Wookies are one of them) - all brought by the Tho Yor. That said, I'm more interested in letting people play characters that interest them, than adhering to Legends. But THAT said, what is an Echani? :P
I don't have the sourcebook for them, nor are they listed in any community resource I have (though I haven't updated those resources in months and months). You can play whatever Species you would like as long as it's from a published sourcebook, though we'll have to change/gloss over/ignore their official background if it they "shouldn't" exist in 25,000 BBY.
As I don't have any resource for reference, if you decide to play an Echani, could you just PM me their vitals?
Also, please do poke around on the forum to check out the IC and OOC resources, and to get up to speed on the IC story thus far.
And actually as I think about it, I do have a way to bring you in fairly quickly, so if we get your PC ready within the next couple days or so we can probably get you in game...
+100 post-chargen XP
+1,000 creds
+1 Force Rating so long as your Morality is between 30 and 70 (Tython is a powerful Bendu Nexus)