There are plenty of guides out there but I see nothing on this Cheevo so I thought I would summarise how I got this in short and answer any comments questions that came up.
Some high level pointers.
Do this in Jacked Mode. 1 & 2 man missions are impossible in classic mode. Jack is a god send in staying cloaked, opening torture pods and picking up cases etc. (plus mid game Hijacks of Boomers and Theron Guards!
Equip your squad for max damage output. All with UIR gear for Grenade blast and cool down. Forget armour that boosts health (you will still get one shotted) Snipers are all about Crit chance and Crit damage.
You may want to save up some tokens to re-equip your team for the final fight with ukkon. I got swamped after 1 hour of playing and then aborted and re-skilled my squad. Gabe NEEDS Surge.... being able to reset Jack's cool downs for a clutch hijack or shock WILL stop a boomer or Flock of Grenadiers wiping you out (one shot kills from those bad boys)
Do not worry about optional mission objectives if they put you at risk. I avoided 2 man missions at all costs until i had level 5/6 scouts. Those 2AP Scavengers runs missions are impossible on Insane without Level 7/8 Scouts.
Deal damage, don't rush to uncover the fog of war and get Disrupt on your WHOLE squad so you can control Grenadiers reliably with overwatch (knockback and interrupt). Stick to full cover and scout ahead with Jack to hijack an important unit to blow himself up!... Get a strong position and send Jack to uncover the fog of war so the enemies run to you and deal with your overwatch kill box..
So that is a few pointers to tackle Insane with no deaths :)
Feel free to post questions about specific load outs I used etc and I will stay close and answer them.