The servers have now closed, therefore the Platinum is unobtainable if you didn't get the online trophies before that happened.
-Estimated trophy difficulty: 7/10 Platinum Difficulty Rating - PlaystationTrophies.org
-Offline breakdown: 46 (34 11 1)
-Online breakdown 3 (3) However, many more trophies are easiest done online. - Unobtainable.
-Approximate time to : 26-35hrs+
-Minimum number of playthroughs needed: 1
-Number of missable trophies: 0, none.
-Glitched trophies: 2; Chanteuse, Sampler Plate.
-Do cheat codes disable trophies? No.
"Chanteuse" may be a glitched trophy, depending on whether you get 100% of the notes on the song, or if you get 6/5 gold/non gold stars. These somehow conflict with each other.
For "Sampler Plate," you may not get credit for achieving the trophy even though you've played through every game mode. If you've played through them all and it hasn't unlocked, play them all again and it should unlock.
Step 1: Career Mode
Simply go through career and play all of the songs, while attempting to get 5/6 stars on the songs and possibly even complete a few challenges while going through the set. This should net you a majority of the trophies in the game.
Step 2: Multiplayer - Boost/find other players in order to get the trophies. - Unobtainable
This can be most helpful with getting band challenges if you cannot earn the trophies locally with your nearby friends. This should net you a lot of stars and challenges, and should also be mostly looking out for the 3 online-only trophies. You should also be concerned about getting the "4 of each instrument" trophy too if you cannot accomplish that by yourself. Find the boosting thread for this game at this link: Trophy Boosting Thread (Read First Post!) - PlaystationTrophies.org
Step 3: Cleanup
Go through career and get any remaining stars you need by doing challenges and scoring as many stars on songs as you possibly can. It is also a good time to play 300 songs in quick play if needed. The easiest method for getting 300 songs in quickplay is by creating 10 songs in the music studio that consist of one short 3 second note, and making a setlist of these 10 songs and playing them in a setlist over and over until the trophy unlocks. This should get you the trophy much quicker then trying to play 300 normal songs over a long period of time.
[PST Would Like to Thank Whiteclone for this Road Map]