
If you aren't Doman, or Othardian, then you could be trained by one. Or you could be trained by someone who was. Lady Yugiri also states that they'll start training allies of the Scions in the arts (I'm not sure if this was the Grand Companies as well or what), and Oboro says they'll work with the Lominsan Rogues. The style of combat is very similar, it's really the magical aspect that sets Rogues and Ninjas apart.
I haven't seen anymore limitations to the class rp wise than most of the others, and how you use the mudras is up to you, they're generally less flashy than what a mage class will do
. Lore wise, the Shinobi don't advertise who and what they are anymore than the Rogues do as that could be a tip off in the targets favor.
As for how many master ninja are out there? Well if they're masters they aren't going to tell you that
but as far as learning goes, post 50 there aren't anymore mudras to learn, and all the skills are self taught through the questline.
I haven't seen anymore limitations to the class rp wise than most of the others, and how you use the mudras is up to you, they're generally less flashy than what a mage class will do

As for how many master ninja are out there? Well if they're masters they aren't going to tell you that

~~ Not Primals call nor beastmans roar, Empire's wrath or nature's thorn... ~~
~~ Through gloam of night and scorching day, even weathers pour will naught bar our way... ~~
~~ With honor and pride, our tasks be swift done, a courier's path is ever run. ~~
~~ Through gloam of night and scorching day, even weathers pour will naught bar our way... ~~
~~ With honor and pride, our tasks be swift done, a courier's path is ever run. ~~