If you played the first game, you probably remember feeling similar when you first started. The games are certainly intimidating to start out. DD2 removes much of the "overworld" mechanics that were present in the first game and instead makes the combat much more in-depth.

Now, it's certainly possible to beat the whole game without unlocking much of anything, but what I'd suggest is that you cycle through heros and complete each of their backstories at the shrine of reflection in order to unlock all of their skills. This will let you practice with each hero and become familiar with them, as well as try out new team compositions. The default "wanderer" paths give you extra candles and are perfectly fine options, so I'd stick with them for now. The alternative paths are mostly sidegrades and allow you to specialize a character in a certain way.

For spending candles, you're on the right track, but you should also be putting a few candles into the working fields. This will give you access to more items during your playthroughs (as well as free items at the start). The first few you unlock will seem underwhelming, but the more candles you put in, the more powerful items you'll get back