I suggest you refrain from talking about things you don't know.
In the current climate, I would say Milan tickets will be easy to come by. We haven't sold our allocation in the last two trips (Milan and Inter) and there have been returns as well as spares even on the day. All the reds I've known that have made the trip ticketless have had no problem getting in.
If you are willing to go, the tickets should be your final concern. Don't even consider paying over the odds as there most definitly will be plenty spares in Milan if you won't be able to have something sorted by then anyway.
The 1% is usually a bitch
For Euro aways you just need an OU membership and to have registered with the Travel Club.
Definitly not GS. Many will apply to get the credits so they can use them later on should we progress, but many won't make the trip and there will be returns and spares.