The naval staffs' plans included having the A-H fleet based out of Augusta with the Italians at Messina or (more likely) Naples. Both navies planned to be a lot more aggressive as allies than they turned out to be as enemies.
The RN had a long-term plan that would see the 7 oldest dreadnoughts based in the Med, but this was not meant to be until 1917.
Why is the Spanish Fleet involved?
The British fleet is going to take ALOT of losses by going that direction. Is that going to be palatable enough to the British public to keep the government from falling? Hell three old cruisers were sunk in the Action of 22 September 1914 and the public outcry was fierce.
I agree. The French start with 2 dreadnoughts and 6 semi-dreadnoughts and a lot of armoured cruisers, but would be outmatched by combined Austro-Hungarian-Italian fleet. If we assume the same dispositions as OTL - and as no-one knew what Italy was going to do I don't see why not - the RN would have 3 battlecruisers and not a great deal more, although 4 modern armoured cruisers would probably join from the Red Sea. We know the early battlecruisers appeared to be the supreme force in the Med but in hindsight they were unlikely to come out well of any encounter with even the earliest Italian & A-H dreadnoughts. They will probably start by moving a large number of pre-dreadnoughts to the Med - certainly
Agamemnon & Lord Nelson, unlikely the King Edward VII's "wobbly eight" as they were on the Grand Fleet roster.
So not sure the Entente could muster enough ships to ensure naval superiority over any landing zones that would last to maintain supply across the beaches. It could be a reverse amphibious operation that happened, as the Italians had plans to storm ashore at places like St. Tropez and turn the French mountain defences, but they would face the same problem if they went for this or a descent upon Corsica.
Whatever happened, it would be far more interesting & far more costly than OTL.