If the Austrians attack before the French expeditionary corps has arrived, it can be a problem (but not necessarily a disaster: French mobilization was effective and quick, and the use of railways to bring troops to the Piedmont border was very innovative for the times). It would also necessitate a much, much better C-i-C than Giulay (who was obviously well above his level of competence): problem is that there were no suitable candidates, and anyway the top-slots were awarded by seniority and social status (an arch-duke will always trump anyone else for example). Crossing the Ticino and attacking sounds very easy but it is a bit more difficult to put in practice; there is also the non-irrelevant matter of where to attack: in the north, towards Vercelli and Novara where the Sardinian army was grouping or in the south, towards Alessandria where it could be anticipated the French would concentrate (as it happened, Giulay dithered among the two options and in the end decided to follow the suggestion of his subordinates and wait on the eastern side of Ticino)? Certainly a Napoleon (or even a Massena) would not have hesitated, but Giulay was not on that league (incidentally, it is interesting to note that the lack of "outstanding" generals was not a weakness of the Austrians only: the period between Waterloo and Solferino had been substantially peaceful, with the only real wars being Crimea - where non of the generals involved can be accused of brilliance -, the 1st Schleswig war - do.- and the brief campaign of 1848 in Northern Italy where Radetzky victory was heavily favored by the lack of coordination of his opponents and the reliance on the secure basis of the Quadrilateral. The armies preparation for wars had been reduced by lack of money, no improvement in doctrine and an officer corps who became older and older but had spent too many years rotting in garrisons or carrying out relatively minor police actions. Even the famed Prussian army had degraded a lot, and if the defeat in the 1st Schleswig war had been the first warning bell to start some reforms, these reforms in 1859 were still very much a work-in-progress).
The tactics employed in 1859 were practically the same as in the Napoleonic wars, with only minor improvements in small-arms (Austrian army) and in the use of artillery (French army, with a doctrine of fire by batteries and not individual guns): however the main infantry tactic was still the shock column with bayonets; the Austrians never evolved a better doctrine for infantry to fit their improved small-arms, and did not learn anything even after 1859 (in 1866 the Prussian infantry tactics were much evolved, with emphasis on individual squad action, learnt from the reports of Solferino and tested in the 2nd Schleswig war; the Austrians were still stuck with shock attacks, and the only improvement was the adoption of battery fire).
I would believe that the possible intervention of Prussia and the other German Confederation states as game-changer in 1859 is overestimated by an order of magnitude at least. First of all, the armies of the minor states in Germany were not very large (Austria was certainly not in favor of any of these states fielding large armies, and anyway there was always the problem of funding armies which were not expected to be used), and coordination between these armies under the umbrella of the German Confederation was minimal (the same problem happened in the war of 1866, where the Prussians felt entitled to run significant risks in their campaign in western Germany because they had correctly evaluated the lack of effectiveness of their German opponents). Prussia had certainly a much larger army (which however was still being reformed), but did not have any particular urge to save the Austrian bacon (the humiliation of the Punctuation of Olmutz and the consequent dissolution of the Union of Erfurt was still very galling for Prussia): in any case the Prussians made an attempt to mobilize, as requested by the articles of confederation, but between the lack of a strong political will and the half-baked status of the reforms the mobilization was very slow and chaotic.
In particular the biggest blunders happened with the use of railways to move troops toward the Rhein. In a way it was a lucky failure: the General Staff (under Moltke the Elder, who in 1859 was not in the strong position he would be in 1866, much less in 1870) concentrated in the post-mortem on the reasons for the failure of the mobilization. Once again, 1864 was the test for the new arrangement and 1866 was the demonstration that the Prussian General Staff had been able to debug this issue.
In 1859, however, the first Prussian troops started to drift along the Rhein in August, when the war in Italy was already over.