Insanity actually feels easier for a majority of the game. A few assignments are a pain in the backside on this difficulty but it isn't too difficult.
My Shepherd was an Earthborn/War Hero backgroind and I chose Adept as my class.
I had 12 in armour, pistols, charm, lift and Spectre training by tje end of the game. Make sure you have one point at least in all powers for related trophies also.
Spectre gives you master Unity, which is invaluable, as is master lift as it can save your life against certain enemies e.g. Krogan soldiers. Singularity is also a good choice to have at least advanced singularity in as it can throw whole groups arlund the battlefield.
My Squad was mainly one of two options Ashely and Tali or Ashley and Garrus. Two reasons for this, one is for Geth related missions, which Tali is really useful for, especially with master AI hacking. and Garrus for when I needed extra combat muscle.
Before you get to that though make sure you use ALL squadmates for five missions/assignments each before using the same two or three for every mission.
Explore uncharted worlds fully as each collection you complete gives you a ton of XP as well as complete assignments towards the Completionist trophy.
Here are the assignments I completed.
Citadel: Old Friends
Citadel: The Fan
Tali and the Geth/Tail's Pilgrimage (Starts as UNC assignement Geth Incursions)
Wrex: Family Armour
Citadel: Asari Consort
Citadel: homecoming
Citadel: Jarleed and Chorban
Citadel: Presidium Prophet
Citadel: Reporters Request
Citadel: Rita's Sister/Rita and Chellick/Rita is safe
Citadel: Scan the keepers
Citadel: Xeltan Convinced
Citadel: Signal Tracking
Missing Person/UNC: Privateers
Citadel: Family Matter (after two main missions finished)
Citadel: Planting a bug (after two min missions)
Citadel: Snap Inspection (after two main missions, may not show up in journal)
Feros: Power Cells
Feros: Varren Meat
Feros: Water Restoration
Noveria: Espionage
Virmire: Kirrahe's Team
Virmire: Wrex is Convinced (where 12 charm comes in handy)
UNC: Prothean Data disc
UNC: Valuable Minerals
UNC: Signs of Battle
UNC: Turian Insignias
UNC: Asari Writings
A Person of Interest/UNC: Hostile Takeover
UNC: Dead Scientists
UNC: Colony of the Dead
UNC: Geth Incursions
UNC: ExoGeni Facility
UNC: Espionage Probe
UNC: Missing Marines
UNC: Cerberus
UNC: Hades Dog's
UNC: Derelict Freighter
UNC: Distress Call
UNC: Lost Freighter
UNC: Lost Module
UNC: Major Kyle
UNC: Missing Survey Team
UNC: Besieged Base (75% Paragon required to unlock)
X57: Bring Down the Sky
X57: Avoid the Blasting Caps
X57: Missing Engineers
The above plus the main missions of Eden Prime, Feros, Therum, Noveria, Virmire and Ilios will net you the completionist trophy. I missed quite a few of the harder combat ones such as UNC: Hostage, for example, which has an annoying amount of biotics running around like nutters in close quarters.
I made sure I took every opportunity to be nice to get 75% paragon for an extra assignment. This also helps to pacify Saren in the final battle arena so you only have to fight one boss and not two.
My save file was about 22hours in total. Plus a casual run for one trophy I realised I wouldn't get so took my 24hours in total. Much quicker than the original list.