I came into four copies of the core set and those are the only cards I have available to me. I have ordered and am waiting on two copies of assault on ulthuan, 3x warpstone chronicles, and 1x arcane fire.

Here's the deck:

2x Crooked Teef Goblins

3x Squig Herders

2x Followers of Mork

1x Boar Boyz

3x Lobber Crew

3x Servants of Khorne

3x Savage Marauders

3x Festering Nurglings

1x Nurgle Sorceror

2x Chaos Knights

3x Savage Gors

1x Bloodthirster

2x We'z Bigga!

1x Pillage

1x Troll Vomit

2x Seduced by Darkness

1x Flames of Tzeentch

1x Blood for the Blood God

2x Choppa

3x Shrine to Nurgle

3x Contested Village

3x Contested Stronghold

3x Warpstone Excavation

3x Innovation

2x Chaos/Orc Alliance

I honestly have no idea what I'm doing.

Its a terrible deck, but you know what, whocht he sets you got, do not worrey about that. Just throw together an order deck, get a friends and throw down. You will have lots of fun, just play and you will quickley see what works, and what works better.

You can learn somegreat decks here, but really, its a lot of fun to just play and learn, they start upgrading.

What makes a deck good? Generally should you always take 3 of any card you deem good enough to include (assuming you have them available)?

Is it extremely limiting to work from only the core set?

I see the term 'single set' thrown around a lot, which I presume means one of each released set and battle-pack.

Single set does mean a single copy of each set/pack/expansion. It was fun during the Corruption Cycle as Battle Packs still had singletons in them and the regular competitive format had grown stale. Since the beginning of the Enemy Cycle though, each release has included a full play set of each card. I'm sure had FFG not decided to change, Single set would still be very popular - But it is hardly ever mentioned any more.

If you are looking to build competitive decks and do not have 3 of every card, you are obviously at a disadvantage to those that do. If you're playing with friends, but still want to build competitive decks, you can use deckbox.org to see the cards and make proxies.