None of these cards are actually required to make this deck work. You can build you own version by keeping these ideas in mind:
Balance skill is unnecessary. It's used to increase the chance of getting Polymerization or Fusion Sage in your starting hand.
Your starting hand will reflect the card balance of your deck.
You can use WATER monsters to make a beatdown deck by swarming the field and simply relying on their high attack. It's relatively cheap to make since many of them are low rarity or from the card trader. Mako's skill - Mythic Depths is recommended to used in this deck too.
Auto decks are decks that are mainly made to be used with the "Auto-Duel" function. The reason why people often want to go with Auto-Duel is simply because it is done much faster than manual play, since it is fast forwarded and easy to use with just one button. Keep in mind that win rates for auto decks vary depending on what level of Standard Duelists you are going against.
Some decks are made to have a high chance of winning and ends fast. This is good if you ever want to level a character quickly or buy a "Boosted Duel Orb" from the shop. With only an hour of infinite standard duelist spawns, winning the duels quickly can earn you a lot of exp, levelling a character up quite fast.
The other type of decks are made to get a high score with auto duels. These decks might not have a consistently high win rate compared to the ones made to win, but they can often give up to 3000 or 4000 easily by using auto duel from the start. Earning a lot of points from the Duel Assessment will give more rewards like golds, stones/orbs, and most importantly, the standard gate keys and the colored ones used to farm Legendary Duelists.
2. Which monsters and spells work best
Making an auto deck that's made to just win the duels can be pretty easy. All you need is to put a lot of monsters with high attack like Warrior Dai Grepher or Jerry Beans Man, and use spells that can increase their attack like Banner of Courage, Reinforcements or any equip spell cards like Wicked-Breaking Flamberge - Baou.
3. Check the Duel Assessment page
To make an auto deck that gives a lot of points, you will need to understand first what are the things you need to do to get a lot of points. Take a look at the Duel Assessment section. Make an auto deck that can tribute, fusion or ritual to get more points, destroy 5 enemy monsters or be able to summon Meteor B. Dragon to deal over 3,000 damage. Being able to end the duel fast from either turn 1-4 can also earn the quick victory bonus.
AI cannot activate skills manually. That means you will set a skill activated automatically to your auto deck.