I am fine being RubySlipper's brother and that I would not mind he owns a halfling slave who's knees and legs had broken in enough times that she cannot walk much
. Or as Warlock said; trips all freaking time on her long hair (for comedy effect).
Anyways to comment on Kunoichi's build; The devoted tracker feat demands that you got smite (something)
as requirement and mount
class feature to get any use out from it. Wild empathy and track also needed but you get those being ranger at all.
Now, you got mount class feature with your variant (and animal companion via beastmaster, clever move btw). However to get devoted tracker you need take single level dip onto any class which gives a smite ability. Or gain it via race/template.
Now, paladin of tyranny is about being lawful evil. A slave could had devoted it's faith to be a slave; meaning she respects authority in strict sense of the word. So she would not defy her thayan masters but rather be loyal servant/slave.
Now race/template: Fiendish creature is quickest way to get smite good without paladin conduct shehanigans, but it's crappy +1 LA template but you can buy it off with UA rules (so you start bit slower with being 7th level but you should quickly catch up as it costs just 1,000 XP remove +1 LA). Background wise you may have distant fiendish ancestry (common in Thay) or you were summoned from evil plane and brought to prime material plane as slave.
Another a interesting approach is using devil (or celestial) bloodline. However it comes with expense that you get no class levels in 3th and 6th levels (but they count otherwise as 'level' so you get bonus feats and stat bonuses but no BAB, saves, skills, HD etc but it progress CL or using class features like smite). But in return you get stat bonuses and bonus feats and some resistances and skill bonuses.