Well, I'll try to answer your questions as I see it on how to build a deck.
A) You typically put in 4x of cards so you can more accurately ensure that you will draw into that card. If you only have 1 of each card, then your chances of actually drawing that card is a lot lower in terms of percentages. For higher cost cards, say 5+, you don't need 4 of, because you don't need to card until at least turn 5, so you can possibly only put 3 of each in. You never want to be in a situation where one card is going to win you the game, but because you only have one of them in your deck, you might never draw that card, or even worse, you already played it, and it now sits in your graveyard with no way of retrieving it.
B) Quests are more of a personal preference. I play a minimum of 12 quests per deck. The advantage of using quests is that is allows you to gain advanages in other ways, usually for a low cost. Being able to draw cards, or search through your deck for a card you need is invaluable. Now unlike MTG where you can only play lands as resources, you can play any card as a resource, but if you don't have quests, you have to decide on some other card that you don't need, or are willing to sacrifice to be used as a resource. If your playing a rush type deck where you expect to win by turn 6 or 7 every time, you can lower your quest amounts, but if your playing a control type deck where you need to go into the further rounds, you will want more quests that will allow you to keep your ability, allies, and weapons or armor cards in your hand for play rather than being used as a resource.