best advice I can offer you is to wander over to the Paradox forum and read some of the PoN AARs that are being written. The link is here -
http://forum.paradoxplaza.com/forum/forumdisplay.php?559-AGEOD-AAR-s
(you don't need to register with Paradox to read them, but you do need to register to add comments over there)
In particular there are a couple of Sardinia-Piedmont/Italy ones that discuss the economic model in some detail. Not claiming the solutions reached are optimal, but both AARs (one is mine) show a route to stabilise the economy and start on the road to economic development.
Other than that, ask specific questions here, you'll get useful responses.