Be at a decently high level.
For dead money, get familiar with the crafting systems and careful looting. It's more of a survival horror. Alot of people hate it because it requires you to use your brain and isn't an ADHD merry go round. Use the cosmic knives on the enemies as much as possible they require dismembered to actually kill, and the cosmic knives have the highest chance.
Honest hearts can be challenging or a walk in the park depending on how much you want to scavenge and how much you've put into the survival skill. Lots of big enemies, like giant cazadors and poison geckos and yaoi gui. It can also be the biggest game breaker game play wise but we will get into that later
Old world blues is the most overpowered Dlc in the entire game. If you play through and scavenge and do all the side quests and visit everywhere you'll be literally unstoppable. You have robots that make endless crafting supplies, robots that give you clean water endlessly, a garden, and a machine that will take whatever plants you give it and turn it into other plants that you can use to make stim packs (honest hearts has an absolute shit ton of plants, if you take all the plants you gathered from honest hearts, you can make like 800 stimpaks, and they also grow back). You can get a body part that completely gets rid of poison making you forever immune, body parts that no longer get crippled, and OP cyborg implants, gameplay perks that make cazadors a bunch of soft little bitches. A overpowered stealth suit. Overpowered weapons and gear. It's actually insane how unbalanced the DLC is. It also added overpowered perks like the Thems Good Eatin, and Jury rigging if I'm not mistaken too. Thems Good eating gives you a 50 percent chance for two healing items called blood sausage and thin red paste to be in the inventory of enemies you kill. They alone are good healing items and can be sold for 125 to 175 caps each. With a few easily found crafting items you can make thick red paste and black blood sausage which do even more healing and the black blood sausage sells for like 350 caps
Then there is the infamous lonesome road. That dlc is hard, like really hard. Only go do when you're a high level and have done the other dlcs. Bring lots of rad away, healing items, tough armor, and your best weapons and gear. It loves throwing OP death claws and NPCs with overpowered weapons and gear at you. It's also the only place in the entire game where a nuka cola quantum will spawn