DeweyCrowe
and I can't really figure out where the hull should go.
Ah, you are referring to the waterline.
Welcome to the joys of model ship building.
The easiest thing to to find, in the instructuctions some sort of side view, and measure up from the keel on the drawing, and two points on the drawing you can definitively find on the model.
Measure those points on the model, and used that to get the scale of the drawing used.
Prop up the kit in some sturdy way. Stack blocks of wood, or set a compass, to the waterline height, and then draw the line raight around the hull in pencil (or use a needle to scribe a line).
Now, what to paint below this line is not "settled." There was a time, roughly after carracks were common, when "whiting" was applied to the hull. That might just be white lead paint. It might be tallow and ground lead, or tallow over lead sheeting--any of those, possibly, covered in thin sacrificial planks.
Equally likely, especially in the era of Carracks, would be a black tar coating. Most of out history on those vessels are from tapestries, pottery, the occasional painting. And, some have no underwater color shown at all.
And, the "at rest" waterline might not be appropriate, too. If you look on the kit, there will be a moulded-in set of thicker planking, that's a "wale" and the thicker planks were to give structural strength to the hull. Some underwater coatings went right up to the bottom of the wale, as that might be wetted as the ship leaned over in the wind.
But, there's not really a hard and fast rule.
Not a lot of cameras in the era before Columbus, so, anyone who says your choice is "wrong" will be hard pressed to prove it. (That, and it's kind of rude to tell you how to finish your own model.)