All he really needs is the coast. The rest he probably would want the Austrians to rent farm for him. Much like he did everywhere, where he had the countries pay for occupation troops, for battalions to contribute to his campaigns, and for the officers who abanondin end him once he had given them lands, money, titles, and everything to lose if they kept supporting him when the chips were down. Anyways, I think the borders would be fairly different, given how often they changed as he made countries into republics than kingdoms then traded the land around again.
I imagine he also does what he did IOTL, which was to to continue the policy in the Croatian Military Frintier to not draft the populace or tax them, but to keep them all Trainin Incase of war with the Ottomans. Maybe continue or expand it to the Slavonian, Banat, and Translyvanian ones.
Side note. In case of him breaking up Austria, most of the stuff from their churches, palaces, banks, etc end up either in the Louvre, in the mint, or in the jewelry box of Nappy's wife. Not sure if they kept robbing churches during the Imperial Era, but some clergymen wisely gave a sapphire talisman with two pieces of the True Cross (TM) to him when he showed interest. It had supposedly been taken off the body of Charlemege himself years before. It ended up as Josephine's bracelet during the coronation.
EDIT: Come to think of it, what about France, which had the same monarch as Italy, tried folding the Illyria into Italy?