Newly revised timeline. Tell me if I've screwed up any important details:
Seems rather good to me. You screwed nothing IMO, but left out some significant details that need to be defined:
It is better to tell explicitly that the crown of Italy goes to Charles Albert of Savoia, and that federal Italy is a liberal constitutional monarchy on the German model.
Likewise, is Hungary still a liberal constitutional monarchy or republic, and if the former, who gets the crown (Liberal Habsburg scion ? Magyar noble ? Cadet scion of European royal house ?) They might become a republic, but this would single them out from all their neighbors, and further alienate Russia. I suggest they pick a monarch for this reason.
Moreover, I assume Austria and Bohemia-Moravia join the German Empire as one united Kingdom of Austria-Bohemia, or two Kingdoms, whether in personal union or not. It is useful to define this detail because it has some significant influence on the internal politics of the German Empire. If it is one state, it is the option more satisfying to Austrian legitimists and make the Austrian and Bohemian Germans most happy but it makes the Czech most unhappy and makes this Kingdom have an influence almost rivaling Prussia. If there are two separate Kingdoms in personal union, it is the most traditional option of all, so it still makes Austrian legitimists somehow happy, but the Czech more happy and the Austro-Bohemian Germans more unhappy. It gives the personal union still some serious clout but somewhat less infleunce. Two separate Kingdoms is the option that makes the Czech most happy and Austro-Bohemian Germans most unhappy. Pick the option you prefer, but since this is a liberal-national German revolution, I would rather go with either united kingdom with a measure of autonomy for Bohemia or two kingdoms in personal union, depending on what kind of settlement Austrian-Bohemian Germans and the Czech would work out, either by agreement of by show of force, during the revolution in Vienna and Prague. The Czech shall need to be bullied or bribed somehow anyway, in order to agree join the Empire.
Also, if Hungary keeps an Habsburg monarch, you need to define whether they continue the personal union with Austria-Bohemia or not. Both options have benefits and drawbacks. The personal union pleases Habsburg legitimists and Russia, but PO France even more and displeases Britain (balance of power and all). Complete independence pleases radical Hungarian nationalists and appeases France and Britain just a little more, but displeases legitimists and Russia.
Last but not least, some ex-Habsburg lands go unaccounted in your description. I suppose the German Empire still gets Bozen and Slovenia as part of Austria, but better to mention it. Moreover, what happens to Croatia in this settlement ? Legally, Croatia was not a traditional part of the Hungarian Kingdom of St. Stephen like Slovakia and Transylvania. IOTL, Slovaks sided with Magyrs and I assume that without Russian intervention, Hungarians easily suppress any Romanian unrest. The Croats fought the Hungarian, but again, without Russian aid and revolution in Vienna, they shall be defeated. What form does the union of Croatia and Hungary takes ? Are they simply incorporated in the Kingdom of Hungary, or is Croatia granted autonomy and a personal union ?
Now, in OTL, the Second French Republic sent some troops over to the Papal States around about this time. What will they be doing now, if the Papal States peacefully unify with the rest of Italy?
Hmm, for the immediate future, they can do little, since in my knowledge they would lack a decent casus belli.
Attacking Germany and Italy with the explicit intent to undo the "free" (more or less; revolution has forced the hand of the reactionary monarchs, but France is not legitimist, cannot use it as an excuse, and anyway the Pope's blessing ruins the argument) decisions of their monarches and peoples, including the Pope, would single out France again as the Napoleonic aggressor of Europe, isolating it from any possible ally, and not be very popular with both liberals and Catholics at home. Both important constituencies for newly-elected President Louis Napoleon.
It is true that this resettlment geopolitically screws France in comparision to its traditional place in Europe, but such cold-blooded realpolitic "balance of power" issues still need to be sold to the people with a decent casus belli to create a decent consensus for war.
I would say that for now, Napoleon is livid but can do little, he officially congratulates Germany and Italy for their successful unification, tries to whip up French nationalism against the "encirclement" of France and scrambles to gain some territorial compensation for France.
Say he claims that to compensate for the unifications, France needs to be compensated with the left bank of the Rhine and Nice-Savoy: of course, both Germany and Italy shall answer a loudest No, and this heightens nationalist tensions in all three countries. However he would not likely go to war about this, lest be singled out as the expansionist aggressor. And/or try to buy
Luxemburg from Netherlands as he did later IOTL, but dunno whether Netherlands would be willing to sell at this point, most likely not, and again he would likely back down since Britain would not support him on this.
Also he would seek out allies in Europe. Approaches to Russia would almost surely be rebuffed since Russia would have little interest to undo the established settlement. Britain holds better opportunities if France is willing to expand the alliance to counter Russian expansion in the Balkans as well (the basic issue behind the Crimean War).
Of course, this would cause a realigning of various geopolitical contrasts and affinities into a chain reaction of rival alliances. Eventually in a few years it causes Europe to split into two rival alliance systems: say Britain-France-Ottoman Empire-Sweden-Danemark vs. Germany-Russia-Italy-Hungary. Spain may stay neutral or join either bloc according to political butterflies, it does not have a strong vested interest toward any.
Basically, early national unifications cause early emergence of rival Europe-wide Industrial Age pre-WWI alliance systems. And almost surely, a proto-WWI General European War sooner or later. The OTL age of the limited wars of realignment is butterflied away since this success of the 1848 revolutions makes it unnecessary. History leaps a stage froward. Hard to say which the trigger may be, there is wide butterfly latitude about this. This may or may not be something in the Balkans (the OTL excuse for the Crimean War was flimsly), the reopening of the Scheswig-Holstein question, a Russian-Ottoman clash, all of the above in quick succession, or something else entirely.