As for unifying Italy... I see how it can be frustrating.
The problem is that all those small Italian nation states were very divided in their loyalties. Some of them are strongly pro-French, others are strongly pro-Spanish. Yet others are clearly friendly to the Austrians.
for unifying italy: start with one or two italian nations that are most friendly to you.
Don't start with Genoa!! Genoa starts the game HATING Venice, because they are historical arch-rivals.
What you should do is to ally with someone else thats at least luke-warm friendly with you, like Tuscany or Modena or Naples or Milan. Then work on vassalizing them one or two at a time. Once you have a strong ally in the Italian mainland, you and your allies can slowly eat away at the "rivals" like Papal states. But do NOT attempt to war with them if they are clearly allied to a huge bully like France.
It's extremely easy for those huge French-Savoy-Helvetian armies to march into Mantua and Venice and give you a bloody nose if you piss them off at the wrong time.
You need to time your wars when you 'eat away' at your rivals. Always look at the ledger to see when that France-Savoy-Papacy-Helvetia grand alliance expiration date. It tends to expire a lot or it falls apart often because they disagree on this or that. As soon as that big alliance "expires", you and your allies can immediately declare war on the lone non-allied nation. They have no allies to call upon, so you can slam them hard if that's what you want.
You can also use the alliance expirations as the perfect time to grab new allies away from France or Spain. This assumes you have good relations with them already, otherwise they obviously wont join into your alliance.
Then once you have some of these small italians on YOUR alliance, never let them go. As soon as your alliance expires, reinvite them right away, so you keep your alliance forever. This will give you many many years to work on vassalizing them one at a time, without worrying that they will switch sides to someone like France or Spain.
Also, be very careful on who else you invite to your alliance. For example, if you invited Spain or Turkey into your alliance, then keep in mind that several of the small italian nations have an animosity for either Spain or Turkey. If there is someone already in your alliance that they do not like, then they will REFUSE to join your alliance.
Good luck, and I hope that the righteous Austrians crush you under their metal-tipped boots. Oops, did I just say that?
