Don't know what the tankage is on a C42, but a watermaker might make up any shortage. Since you want extra cabins and only plan to cruise for a few years and not push the boat too much, what about a used charter boat of appropriate size? Would be a lower cost, but would need more upgrading, but probably cheaper overall.
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.