Dirk, after 18 pages I thought we had answered your questions, however sicne they may have been lost I will repeat them.
Start with the anticavitation plate 1 inch above the bottom of the transom. Ribs don't go round sharp corners to well if you use excessive height on the engine, so don't over do it.
Hyperlon repairs are quite straight forward. Use either bostic 2 pack glue for critical areas or if just replacing things like wear patches then evostick can be cheaper as you don't have to use the whole can unlike 2 pack glues.
If the damage is too much for you then Nick in Lymington is probably your nearest. Have a look at the home page for Ribnet and the links for firms its quite an extensive list.
There is a cruise to the CI in August, coming ?