To upgrade a hero, you need to obtain hero shards. You need 2 shards to upgrade a level 1 hero to level 2, 3 shards to upgrade a level 2 hero to level 3, 4 shards to upgrade a level 3 hero to level 4, and so on.
It is recommended that you choose one legendary hero and slowly upgrade the hero to max level before switching to a different hero. Different heroes require different strategies, so take time to test different formations.
If you plan to spend little or no money in the game, the two most commonly recommended heroes are Davison and Poseidon. If you feel adventurous, you can go with Apollo too.
If you want to spend some money, you can choose Ivan. You can get a max-level Ivan for about $250 if you have patience to do $1.99 daily purchases for 2 months.
If you do not mind spending a few thousand dollars on the game, consider either Zeus or Selene as your starting hero.
The best way to obtain a hero is through hero events.
No, but I am sure you will have better luck next time.
Be sure to read hero event guides.
An introduction to some of the best heroes of the game.
Hohenheim is preferred by many in leveling. For each coin drop, you gain 1 extra coin with Hohenheim at level 1 and 5 extra coins with him at level 7. When leveling, remember that Hohenheim's ability is only active when he is alive, so keep him well protected.