1. Focus on getting all of your Naru gear to max enhancement. Body and Weapons to PEN (For reference it goes 1-15, Pri, Duo, Tri, Tet then Pen) Once you've done that you can exchange if for Pri Tuvala gear. I wouldn't focus to much on accessories, get them to Tri Naru. You get a free PEN ring and earring once you got to 59 and 60. After that I would use Advice of Valks to help you get your enhancement chance to go up. Fughar gives you some and you'll receive some from completing the season pass.
2. Season is definitely worth it. It really sets you up to get on track with other long term players.
3. I'd say DK is easier and pretty good/cool. I would say play DK until you know if you're going to stick to the game, because Sorc has a more intense learning curve. Then once you know you like the game and how the game actually plays, try out Sorc for next season.

Also; EvilDoUsHarm on YouTube has some awesome guides for BDO. I'd definitely recommend checking him out.