Why for the Netherlands? Basically what happened there was that the prince of Orange landed on the Continent and started moving south, gathering support. Under the understanding from BRITAIN (no one else) that THEY wouldn't stop him, and that they would essentially stand surety for his "gains".
The Frankfurt Memorandum would confirm Napoleon gains Belgium. Granted yes, Britain would pull a stunt like this because it would be in their best interests that the Low Countries as a whole is either in British influence or, failing that, not in French control or influence. But yes, if the Accords were agreed to, the Prince Orange would basically be confirmed to the original Dutch Republic territories.
Again. Why? If Napoléon is still emperor, chances are good he's still king of Italy as well. If he isn't, that might be as much of a difference as a Habsburg archduke replacing Eugène de Beauharnais as viceroy. Or it could even be that they AGREE that Eugène is to succeed there (the Allies generally held the Beauharnais in higher regard than they did the Bonapartes. And Eugène got ROYALLY screwed at Vienna OTL).
Again, the Frankfurt Memorandum, even if Napoleon is still Emperor, by agreeing to that, he loses both the territories and most (if not all) the influence in Italy, which includes termination of the personal union between France and Italy. On the subject on the Kingship of Italy being retained however, I kinda see your argument, and there is just as much a chance that they keep the KoI largely intact, to give to either Beauharnais or to a Habsburg archduke, (Either Ferdinand III, if they choose to give Wurzburg back to Bavaria, or Francis, of the Este branch, whose lands were part of the Kingdom of Italy. Honestly, I dunno, but then again, it largely depends on what the coalition members want out of that.
The Papacy LIKELY wouldn't be restored (least in the same form as following Vienna OTL). The Spanish rep, the marquis de Labrador, was the ONLY one who wanted that. Even Metternich was leery of it, but the problem came up with what to do with those lands if the pope WASN'T restored. If they're still part of your Napoléonic kingdom of Italy, it becomes a dead letter. Other option is if the Habsburgs get Italy and the legazioni are carved off as a rump state for Eugène (as was discussed OTL), but since Spain ISN'T likely to be a participant (at Frankfurt) and also Talleyrand (who was one of the supporters of Murat's kingdom of Naples to avoid either the Bourbons or the Habsburgs getting the upperhand in Italy) is absent, while Napoléon is LESS likely to throw Eugène to the wolves than what Alexander I did OTL, so I could see Metternich making his OTL offer to Eugène. (Via Eugène's father-in-law he made intimations of leaving Eugène in place or being willing to cede territories in the Marche if Eugène ditched Napoléon in 1812 already. Eugène refused the offer and when Vienna rolled around, while he was regarded sympathetically, no one lost much sleep screwing Eugène over. And Eugène was too much of a damned gentleman to say anything about it)
I didn't know the only person interested in restoring the Papal States was basically a Spaniard who may or may not be involved at Frankfurt. That being said, while most of those lands would indeed be a dead letter if we keep the KoI, Lazio wasn't, as it was administered directly by France, which wouldn't be the case anymore in a successful Frankfurt Memorandum. If the Papacy isn't restored, perhaps we might see the "Kingdom of Rome" be an actual title with land rather than just the title for Napoleon's son and heir here. If the Habsburgs get Italy, I can see Eugene getting that as a consolation prize. There's also the possibility of Tuscany being carved away from these lands, to be either restored to Ferdinand III (if the Wurzburg thing still happens as per OTL) or even to the Parmese Bourbons (though, IMHO, if Spain isn't likely to be a participant, I kinda don't see that happening.) I still stand with my intentions with French Piedmont and Genoa though, it'll all either revert back to the Sardinian King, or all but Liguria, the latter going to a restored Genoese Republic.