Adding my own experience here. Firstly, this is a totally legit playthrough, but there are ways you can trivialize it.
First, recommend doing all other ME1 achivements in Normal. Complete all missions, enjoy the story and content! This will level you up for step 2. My selected class was Vanguard, which gives a lot of options to complete power-specific achievements, etc. This also relevant in next step. Also, max Paragon or Renegade path (simply always choose either-or option, don't mix in a playthrough)
Step 2 is NG+ Insanity run. As you have already enjoyed all content, you can speedrun all plot missions and not bother with any side missions, no need to stress about achievements etc. You'll be done in a few hours! Specific tips:
- I used Kaidan and Liara as main companions. With 3 x Pull & Throw + Singularity, you can keep almost all enemies disabled at all times! Max these powers.
- Don't forget to equip the best possible equipment and mods. Choose equipment that lowers power cooldowns
- Only place you should stop in are shops, can't hurt to get medigel updrages. These are reset in NG+.
- Keep Barriers up at all times in combat, at least when enemies have heavy weapons.
- Pick the most troublesome enemy (Krogan, Krogan Warlord, Geth Destroyer and Prime etc.) - Pull, Throw, and fire your weapon on the floating foe to push them even more. ALWAYS Pull or Throw a charging enemy, don't let them touch you! Most importantly: in open air stages like Virmire, and final Citadel space walk, you can yeet even these powerful enemies out of the map in two seconds! With all three characters with these powers, you can disable and kill three Krogans at the same time. Even in enclosed spaces, they are unable to attack and you can keep disabling them and chipping away their health.
- Speaking of enclosed spaces: use Singularity to block doorways. Especially good against the most tedious part of Insanity run, the battle against Thorian and his creepers. You can still throw them off ledges, but in corridors, you can make them bounce around like pinballs. Don't let creepers vomit on you! They are very resistant to damage, but can fall down when you shoot them. They then start pushing themselves up, which means you should shoot again. You can keep a creeper or two humping the floor like this way, and they are completely helpess.
- All main mission planets have linear driving stages: Noveria, Therum, Feros, Virmire and Ilos. You don't need to stop or fight at all! Use L1 to boost, fire only the cannon to clear the way. Otherwise, just drive to the end. Even on Insanity, your opponents have 0 chance to even really damage you. No Tresher Maws in main plot ;)
- Saren: intimidate or charm the first phase, can be done even on a speedrun on NG+. Second phase: the only harmful Saren attack really is when he jumps on the ceiling and fires red fireballs. Keep your barriers up, and you'll be done slowly but surely! Don't despair when his shields recharge again and again. That's just part of the game. If he has a sliver of health but full shields, you can slam him into objects to take his last few health points away!
-Save often. There are spots that you may forget to do so, e.g. the Thorian run and Virmire assault do a good job in making you hurry too much. Your squadmates might remind you to save - when they comment that you are clear of enemies, or when downed and they get up automatically without Unity, then you should also be able to save.
To summarize, the only way to die is to: get charged at by a Krogan or Geth Prime, get vomited on and swarmed by Thorian creepers, or get hit by a heavy weapon. Pull/Throw/Neural shock helps with first two. Barrier, and of course situational awareness, helps with the second. Heavy projectiles are very slow!
Have fun!