1. Most skills do nothing. You use only some basic ones. Spring Attack/Tempo Attack, Low Attack, Guard, Careful Attack. Your strategy is to guard when your opponent attacks, and hit them wheh your opponents is shifting to defense.
Advanced tip: it's useful to look at defense of youe skill. Each skill absorbs some damage. If it is Block defense, it will consume shield durability. If it's Parry, it will just use a weapon.
2. For weapon you need something one handed probably to also use a shield in other hand. Like Broadsword. Though some people just go for Zweihander because it hits hardest. Damage is in the description.
For armor tankiest would be Full-Plate or Diamond+Battleskirt. But they are heavy. Heavy debuffs stamina. You'll feel it if you don't have pretty high Endurance. So maybe just use some cheaper lighter body armor and battleskirt.
And you must buy stat raising armor from second town. On your head, feet, + the Gauntlet of Strength can be found as loot if you travel far up and left on the map.
Money: https://androgyny.miraheze.org/wiki/Status/Gold
3. There's an Overrun (or Slide). To trip your opponent you need to bring their stability to 0. But actually you don't want to trip them. Because they'll get up. You want to just keep them on low stability, because they will be forced to stop attacking, while you can capitalize.
4. Huge impact on combat have your stats. Strength to hit harder, Endurance to not lose stamina, Agility to parry more often and not lose balance, Perception to see next opponent stance in combat to predict their moves. And you can get stats with perk points. And bonus points: https://androgyny.miraheze.org/wiki/Starting_Bonuses
5. I heard Mage class is easy to play. I never tried it. I know you must invest everything you can in Magic to be a good Mage. And I heard Oil+Flames work good for damage.