A few things I've noticed early on:
- Money is pretty hard to come by
As you explore the world, investigate points of interest, loot everything that seems valuable--weapons & armor of course, but even junk items that can be sold for a fair price or dismantled into valuable crafting items. If you're trying to collect weapons and armor, keep only the rarest/strongest of them to throw in storage at the earliest opportunity.
You can hold off on buying the diagrams for weapons and armor from Blacksmiths and Armorers until you've padded your wallet up a bit, and don't have to bother buying the weapons and armor they do sell(especially the super expensive bolts for the crossbow, as you can loot more powerful versions from Bandits and the like), or crafting what you've found diagrams for; much of it can be found during your explorations. The only equipment you should ever bother crafting are those belonging to the various Witcher schools, the treasure hunts for which you can initiate by purchasing the maps/letters sold by some of the Blacksmiths, Armorers and other Merchants all over the place.
It is possible to gain more than enough coin to comfortably purchase everything you need in this game, but it requires time; a lot of time in which you'll be overburdened going from one Smuggler's Cache/Guarded Treasure to the next.
- No exp from killing monsters in the overworld (?)
You do gain XP from any opponents you kill, but it's really petty. There are some bigger monsters you'll encounter later on in the game that offer more XP, but you'll still have to cut down quite a few of them to grind levels. Best way to gain XP is by completing quests no lower than five levels beneath you.
- Gwent is hard; most opponents have totally OP cards, and I missed the ones you could purchase from the innkeep in White Orchard so I think I'm super-gimped
Pretty sure you can still win those cards you missed at random from the Merchants you can play around the world. But, just try to build your deck up first by buying what cards you can.
And If you're having too hard of a time, CDPR did allow you to turn down the difficulty of Gwent specifically in a big update not too long ago. The only reason you'd have to turn it up is for a particular trophy, which you can shoot for much later, once you've got an overpowered deck.