I'm not an expert, but here are some educated guesses that might help you:
Nobody really knows until the tickets are officially released. My understanding is that any game with UK fans is expensive and easily sold out because they have no problem with spending a lot of money to travel and support their team anywhere in Europe. This will add a lot of stress on home seats as well because away fans can buy them up.
The official tickets will probably be released 2 weeks before the game for season ticket holders. During this week, most of the good seats will be snatched up. If you are willing to pay 200 to 300 Euro or so, then you can get one of these assigned to your name. The price is ridiculously inflated, but it's guaranteed.
A week before the game, general presales will start. Tickets will be available at Banca Popolare di Milano and Banca di Legnano. If you don't go for the season ticket option, then the banks should be your first destination as soon as you set foot in Milan.
A good thing is that this year I've noticed the online tickets at inter.it finally working. With a little understanding of Italian and some luck, you should be able to get tickets online. (I'm pretty sure they didn't release CL tickets last year online). But this year looks promising because Fener tickets were sold online.
(Online ticket sales will start concurrently with the banks... if you can't be in Italy one week before the game, be sure to be online!)
Finally, you can try your luck one day before the game or outside the stadium. Even black market tickets would be okay because they are letting go of all the extra security after the derby. If you can't get into one gate you can just sneak into the next. (But you'll end up paying a lot if they're sold out)
Bottom line is: If you want peace of mind then go for the expensive option now. If you're budget conscious and a bit more adventurous, wait until the official ticket release. And if you've got a heart of stone, go outside the stadium before the game
. I'm sure other people on the forum have more insight, especially as the match gets nearer, so wait for more opinions - but remember, Liverpool haven't been to Milan in decades, so I doubt anyone can predict how the tickets will go.
There were a couple more questions:
- For accommodation just search online
- To get to the stadium just follow the crowds
Seriously, get down to the nearest metro station and get a €1 ticket. You should see Inter fans several hours before the game, so just get in and follow them to the stadium. If you get lost just ask for "San Siro" or "Meazza" and anyone can point you in the right direction.