That bow looks like it's coming together for you.
Good job.
For the draw, generally 18" would be about normal, but I like to go at half the length of the bow, or a little over. I'll usually tiller it out a bit further, then shoot it unitl I find the draw that shoots the best.
These bows were not the type used from horseback, those are the bows from the great plains, belonging to the Sioux, Cheyenne, Osage and others. These short paddle bows were mostly shot form blinds at close range (as in under 10 yards).
The arrows were long for the draw length, and got up to 30-36" in length, with the majority in the 28-32" range. The extra length helped to steady the arrow as it came around the wide handle.
Sean