Lots of good ideas here. Some odds and ends,
Loading on beams: Yes it's true the mast load is converted to compression by the dolphin striker. But there is also significant torsion from platform wracking. Also a bending moment from leeward hull hydro forces wanting to force hull under the boat (reaction to lateral sail force). Like most boat parts is hard to quantify precisely how it's loaded.
Cost of materials: For cut yardage expect to pay 30-35 us dollars per pound for carbon. For an entire roll (100 yards) expect to pay 15 dollars. Often you can find a partial roll of 30 to 80 yards at a good price.
One piece method: If you can get it off the mandrel great. Just be sure to do a test to make sure it will work before commiting lots of material to a part that is permanently stuck on the mandrel!! Also need to consider the fit of the new beam in existing beam channels in hulls - the two piece method allows you to almost exactly match the original beam size.