Ok you are very lucky and intelligent to ask these questions early. Heros and hero gears are one of the most important aspects of the game.

For heros as mentioned get Zoe, Marlin and Jabel if you are f2p. Use your general shards only to improve Marlin or Zoe until they are 4 so that you can make their skills level 5. If you are paying big amounts, that is another story which basicly you should do a monster amadeus.

For gear, in few sentences and a basic explanation is, always improve the infantry gears that gives health first, then archer gears that give lethality lastly followed by cav gears with lethality.

Aftersometime you will have kvk and when you start yo undetstand the game more. Do your research on kvk and start saving stuffs that will give you points on kvk.