Sounds like a nice idea. Im not sure though, with an Inca theme being as precise as you want it to be, that Tomb Kings are the way to go. Mainly i think because the fluff you want to stick to eliminates many of the best TK units (Chariots, Scorpions, Catapults)
I hate to say it, and may get quite a bit of backlash, but i think Vampire Counts may be the way for you to go.
Firstly, spear armed skellies are poor in a TK army, whereas in VC then are more worthwhile as you can increase on unit size. Therefore your spear weapon matelral fluff would be more suited.
Also things like their fell bats (condors) and you should be fine using carrion for the models.
As for the resy tou could use many models to represent your characters, so there will be more choice for a look to your characters there, as almost any character can be made to look VC with the right paint scheme.
Admittedly you still wouldnt be using their cavalry, but they still have some other nice units to choose from.
Just my opinion, but i think if you stick to your fluff with a TK list, it will be quite poor.
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