Arena keys and corresponding wins

Spells should always be favored over minions when constructing arena decks. Especially if the are really good and cost effective damaging spells like swipe.

Swipe means 4 guaranteed damage to any one, for only 4 cost + you get to deal 1 damage to everyone else + it has great synergy with spell damage

How many are too much? You cannot use swipe the first 3 turns and if you have alot of swipes and not enough draw cards, you will run out of cards fast. That is the most common reasons for losing in the arena.

For a balanced deck your arena should have about 5/30 draw cards at least 10/30 normal minions at least 5/30 other spells

So you can have about 10 swipes and still have a healthy balanced deck

Edit:
Cost effective usually means several things: You spend less mana to take out a higher mana card and/or you are able to do a 1 card for 2(or more) swap. Swipe can accomplish both in the right situations And the fact that you can use it against heroes makes it a good finisher in a pinch. z-

This depends on time available and skill.

Infinite arena is considered the best way to get cards and dust. However, even assuming you can consistently get 7+ wins, it's bad for actually earning gold. 7 wins typically earns you between 150 and 180. If you don't factor in the free pack and the bonus prizes, that's 10 games, drafting time and risk for less gold than the 3 games/10g.

8 wins isn't much better, 9 is actually worse (you get more cool stuff) so you'd really need 10 wins in a reasonable number of those 7+ runs for it to be worthwhile.

On the plus side, infinite arena is actually infinite. There's no cap so you could play 24/7 if you want.

Quests are the most time-efficient method. Assuming you are capable of using at least 5 classes, you can reroll everything to get Domination quests and get 60g most of the time. Assuming a 50% winrate, this takes 10 games to earn 60g+20g for the 3 wins quest if you play an extra match.

Timewise this would take about an hour and a half, assuming just under 10 mins/game.

Once you've beaten your quest, your only remaining option is the 3 wins quest. This is slow- earning you 10-20g per hour. However, you can use it to supplement the quest rewards. The method above earns you 540g per week (80/day) so winning another 6 games pushes this to 100. This is enough for 700/week or enough to buy naxx wings as they are released.

Since you can play whatever deck you want here, this may be quicker than winning the quests. About an hour, probably. In total, that's two and a half hours a day.

So, to summarise, reroll your quests to 60g, beat those then beat the 10g/3 games quest to make up the rest of the money you need.