any veteran players can advice me what to focus first?
You want at least some attack all. I would recommend multiple. Also a tank and a healer as well as a good single target damage dealer for bosses. Anyone else feel free to chime in if you'd like. I don't claim to have it all figured out. This is what's gotten me to hard 4-9. Turtles are the best tanks. Foxes and fairies are good early healers. You could probably get by with an earth elemental legendary tank with a physical team, but turtles generally have skills that are better suited to tanking and higher defense and constitution.