It's always a good time to shop
During your journey, you will find many dwarf workshops. If you've played the prequel, you probably know that they can be teleported. Therefore, they are always nearby, as long as they have access to a workshop. If you explore the locations thoroughly, almost every workshop you encounter will be worth paying a visit.
There's no point postponing the upgrades, it's better to get them as soon as possible. You should have a lot of money anyway, especially later in the game, so hoarding isn't particularly worth the effort. It's advisable to always have your character upgraded with the latest unlocked weapons, gear and skills in order to match the level of enemies.
Also, whenever possible, get the Resurrection Stone. It's invaluable in more difficult fights. You can only have one at a time, but if you use it up and then die, it will be back in your inventory (if you had it at the checkpoint save).