Filling up your questions that the others haven’t addressed:
1: I guess this statistics is what you want by saying “performance of gauntlet”:
12 - 0: top 0.02% of all gauntlet runs
12 - 1: top 0.17% of all gauntlet runs
12 - 2: top 0.65% of all gauntlet runs
11 - 3: top 1.12% of all gauntlet runs
10 - 3: top 1.93% of all gauntlet runs
9 - 3: top 3.27% of all gauntlet runs
8 - 3: top 5.47% of all gauntlet runs
7 - 3: top 8.98% of all gauntlet runs
6 - 3: top 14.45% of all gauntlet runs
5 - 3: top 22.66% of all gauntlet runs
4 - 3: top 34.38% of all gauntlet runs
3 - 3: top 50% of all gauntlet runs
2 - 3: top 68.75% of all gauntlet runs
1 - 3: top 87.5% of all gauntlet runs
0 - 3: You probably should just buy orbs
e.g.: you went 8 wins and 3 losses in gauntlet. Amongst all gauntlet runs, the performance run you just did is about top 3.27~5.47% of all gauntlet runs.
Looking at this, it’s actually quite an achievement to score 5-6 wins within 1 gauntlet run.
2: IIRC it rewards 1 orb from both sets, chosen randomly.
From what I remember, going 3-3 in gauntlet gives 1 orb and ~30 gold, plus bonus gold or spirits (same as Hearthstone). Going 5-3 gives 1 orb and ~50 gold plus bonus gold/spirit. In other words, a gauntlet run is worth it only if you could average >5 wins - which takes a lot of experience and luck. If you’re averaging 3-3, then I don’t recommend you doing gauntlet - unless you really enjoy doing it.
Hence I’d suggest buying orbs instead, because 1. since you’re new, you need a place to familiarize yourself with all the cards in this game, and 2. games below Gold division feels gauntlet-ish anyways, as the decks you’d face in those ranks is often a makeshift of one’s not-so-sizable collection.
If your primary goal is to grow a big collection, completing daily quests in ranked games should be sufficient.