This achievement is for completing the game on Death Wish difficulty NOT hard diffculty.
Here are some tips for getting started, the early portion of the game is by far the hardest as you wont have any equipment/perks. The game becomes much easier once you have right equipment.
If you are planning on getting all of the other achievements I would recommend grinding those out on lower difficulties and saving this achievement for a 2nd playthrough. once you understand the mechanics and level layouts it really speeds things up.
I was able to pretty much speed run this achievement from start to finish in about 10 - 12hours. I believe I could of done it in under 8 if I wasn;t mopping up the achievements I missed.
You're very first purchase should be the crossbow or suppressor and a sight. Noisy weapons are out they make things much more complicated particularly in the early portion of the game. I went with the crossbow but it depends what you prefer/comfortable with. Don't purchase anything else until you have 5k to purchase the Less Damage perk, the quicker you acquire this the easier the game gets. This makes the difference between being one shot killed and not! Money management is essential early on, the perks for extra med kits, and camouflage will help later in the game.
There is one simple rule to follow if you want to complete this difficulty quickly and hassle free. Do Not Get Distracted, radios, jobs, stash houses and flash points, ignore them all unless you come into direct contact with them. I spent 20 mins on my first playthrough trying to get a radio. Stay focused.
You should have two main aims; complete mission objectives ( immediately) and complete strike points. Why Strike Points? Well not only do they decrease the enemy presence on the map but they provide crucial ally support, being able to recruit help is an excellent method for getting through some tougher missions. However, don't go miles out your way to get every strike point, just the ones near missions will suffice.
Utilise the motorbikes to quickly get from one mission point to the next, and bypass the enemies. Seriously this saves major time. Also, Use your Distract tool, this is a hidden gem which on easier difficulties isn't needed but is essential on Deathwish. Make sure you have abundant health packs, Recruit Allies and Dont get distracted. Use stealth, if like me you use the crossbow make sure you buy the faster reload perk and upgrade fully. If you went with pistol and silencer purchase the perks for that.
Deathwish is VERY doable provided you manage your resources effectively and play stealthily. Bank your valuables, if you die you lose them. Missions provide the best source of income so quickly completing these enables you to purchase the best perks.
If you are struggling remember the early part of the game is the toughest if you can tough it out you'll find it gets easier. I honestly believe I could have completed this in under 8 hours if I wasnt mopping up other achievements. Saving this for a second playthrough really helps, you will understand the mechanics and what to do for the missions.
Deathwish forces you to change your playstyle and to manage your resources and time effectively. You must think and plan rather than go in all guns blazing which is a much more satisfying feeling and It really made me appreciate the game much more.
Hope these tips help you.