What are the chances of prior service coming in under the Try One enlistment-either as the same mos or something different-and being plucked out and sent as 11B, or to fill something else not related to the mos for a long deployment?

Would joining under the mos that transfers from the prior branch served in, limit the chances of this happening?

depends on what your state needs for deployments.i.e. if an Infantry unit is deploying and short bodies than yes they can pull you even if you reclass.