first question- about the twist. I don't have any experience removing twist, but you have 3 choices as i see it- 1. leave it- it might not be twisted to much to be useable- post a pic. 2. after it's at floor tiller stage, steam and straighten. 3. cut it in half and splice it back together without the twist.
second question- I have a BL bow pulling about 45 - a stiff handled pyramid bow. it's 62" long. tips are 1/2 wide. Near fades it is 2" wide. Because of the pyramid design, it doesn't taper much in thickness- about 3/4 near the handle, and about 7/16 near the tips. The rigid handle is 1 1/2 thick. Of course, your bows final dimentions will be determined by long greuling hours of tillering, but this gives you a ballpark.
third question. BL is weaker in compression than most woods, so if you put on a backing, it may overpower the belly. that is, a fiberglass backing does not stretch much, so it would force the weak belly into even more compression. So , i wouldn't back it. In order to overcome the weakness of the belly you can do two things- heat treat it (tempering) , and or "trap" it. Trapping is where you make the belly wider than the back- a trapezoidal cross secton.if your bow will have a rounded back and a flat belly, this is similar to a trapped bow- the back "acting " narrow because of the crown in the wood. In any case make the belly flat, not rounded, and be extra careful to leave no tool marks.
With BL , most people would seal the ends then remove bark and sapwood, then seal the BACK too (not just the ends). BL will check if left overnight with an unsealed back.- then rough out so the limbs are one inch thick at the tips, thicker in the middle (dont forget to leave enough thickness for your handle). At this stage you begin drying. Dry it slowly at first (like a couple weeks outside in a shady cool spot) (if it's very dry where you live wrap it in paper bags to slow the process. ) then, put it somewhere drier and or warmer for a few more weeks. I am impatient and do not dry mine as long as others do. You can do alot of work on it while it's drying- shape the handle, and even bending it a few inches to get it to "floor tiller" . just don't bend it much until it's dry.
If you have a few staves worth- why not take the worst one and make a "quick" bow out of it.... shoot for low poundage and decide that it's ok if it has some set- this will let you work on a not-quite dry piece while the other is drying- will give you a chance to try heat treating, bending, etc...