Start on Very Hard, and stay on Very Hard. It might be frustrating at first, but it is worth it. After lvl 15, you'll be set and can start grinding away at all of the Green quests which will eventually turn Grey. Every now and then you'll do a yellow, but only because it is on the way to something else. After 25, the difficulty turns into a joke even on Very Hard. You'll keep sticking to the Green and Grey quests and you will literally be walking up to them to tap them on the shoulder, and they'll die.
Focus on buying a Legendary Deck first and have at least 5-6 Intelligence (2 Points into the Currency Perk) and you'll never have to worry about money at all since you should be able to hit all 3 most of the time. Back out to change the codes around at the cost of a few seconds of solve time. Just quick save before and after you do each one.
No matter your build, once the map opens up, go get your Epic Char Grenade and your Divided We Stand which will carry you several levels untouched (Just make sure you have a back-up plan for Tygers). You'll get a very decent Smart Tattoo for free from the first mission, get your tech to 18 ASAP and start crafting.
If you follow this, I promise the only time you will be challenged after you have cleared all of Watson is when you have to do something specific in the quests. Stay out of sight, Don't kill anyone, Ect.
*Edit* Unless you are doing the Fist Fights. Bring a bat or sword, set it on the ground, equip it from the ground after the fight has started, and easy win.