Check the classifieds here for cheap osage. Also you can search around for fencepost dealears that may sell osage fence posts. Also look into local sales lists for staves. You could always look to cut your own, or even buy a stave from a sponser like pinehollow longbows. remember to make sure it is dry before bending it.
as for your dimensions, I would take the width at the fades to 1 1/2 for the first ten inches out of the fades or less width like 1 1/4 and taper from there to your 1/4 in tips if you use osage.
A few other woods are black locust, elm, cherry, hophornbeam, hickory, yew... the list goes on. Each wood likes different dimensions. Read up here to find out all you can. Go slow and excersize the bow as you tiller and you should be fine for sure with a few board bows under your belt. AS for a finish i would use truoil.