Sheathing will not remedy broken ribs. You need to put doublers or 'sisters' in alongside them to bring the hull back in to shape, and to restore the strength. The weakness round the mast foot needs seeing to as well, and sheathing is unlikely to make any difference.

IMHO you need to bite the bullet and get the boat repaired properly.

Sheathing? _ what with? If GRP then forget it - it will destroy the boat double quick. Polyester does not stick to wood, allows water ingress which provides ideal rot conditions. Epoxy systems may be possible but will be at least as expensive as doing the job properly, and will require the hull to be dried out to a very low moisture content - around 15% to ensure proper adhesion. That will cause mayhem with your old timber, and once it starts to get moist again it will move further than the epoxy sheath will allow causing all sorts of problems, and quite likely to do more harm than good.

Just a question - have you tried re-caulking the planking? The leaking may be simply the caulking has failed and needs replacing. Assuming she is carvel built that is, and not clinker. A carvel hull will have been built deliberately with gaps between the planks to allow for swelling, and these need to be properly caulked. If she is clinker, then the fastenings are probably loose and she may need re-fastening as you do not caulk clinker.