There has been extensive discussion that you will need 3 core sets in order to have playsets of every card. I've come to terms with that.

Assuming that I want to maintain a complete deck for every faction, how many core sets might I need then? Would I need to purchase additional copies of the monthly packs?

I like to be able to grab whichever deck sounds like the most fun at the moment rather than taking time to build a new deck whenever I play.

Perhaps if we're willing to bring the power level down, then we could make decks for every faction using only 2 core sets? I don't know how much decks you can build before you run out of neutral cards though.

To have a 50 card deck for each faction I think you would need 2 core sets. Someone can check my Math.

30 cards per faction per box. In the second box, 11 would not be useable in a legal deck; Warlord plus signature squad = 9, plus 1 of the 2 ofs, so that gives you 19 faction useable cards which gets you to 48 cards plus Warlord, between the neutrals (you'd have 24) and the extra 2 of cards the allies can't use you should be able to build a deck for each faction.

How balanced and effective they'd be is another question.

There has been extensive discussion that you will need 3 core sets in order to have playsets of every card. I've come to terms with that.

Assuming that I want to maintain a complete deck for every faction, how many core sets might I need then? Would I need to purchase additional copies of the monthly packs?

I like to be able to grab whichever deck sounds like the most fun at the moment rather than taking time to build a new deck whenever I play.

Perhaps if we're willing to bring the power level down, then we could make decks for every faction using only 2 core sets? I don't know how much decks you can build before you run out of neutral cards though.

Based on what I understand of your question, you are wanting to do this long term, including possibly buying extra copies of the monthly and/or deluxe packs?

If you want to do this long-term, the question becomes what you mean by "1 deck per faction". Is this one mono-faction deck, or one deck using that warlord but also using cards from an ally faction?

If you want to make mono-faction decks, you will really need 3 core sets, possibly 4. 4 would let you build full decks that run 2 of each neutral card and still have enough neutrals to keep all 7 factions ready built. If you want to splash other factions, you will actually need *more* to keep prebuilt decks for each faction.

What I mean:

Your Space Marine deck uses a playset of Daring Assault Squad. Your Astra Militarum Deck also uses a playset of them (why wouldn't they? AoE 2 is nice). That means to keep both decks built at all times, you will need 6 copies of this card. If your Tau deck also splashes SM, you could need more.

*Worst* case for keeping 7 full decks ready to play is 9 core sets, but this depends on how you manage your deck design. Mono-faction, 3 core sets would be enough. (You could maybe make some money back by ebaying your extra copies of the faction 1 and 2-ofs to people that don't want to buy extra core boxes)

The wrench in the works at this point is the neutral cards. 2-of in each core set means that 3 core sets gives you 6 copies (a full playest). However, worst case scenario is you needing to include 3 copies of a neutral card in every one of your decks. In this worst case scenario, you will need 11 core sets (!) to have enough neutral cards.

So, Core sets, you will need between 3 and 11 core sets to have enough cards to keep a full running deck for each faction ready to grab and play, depending on your deck construction strategy.

For the monthly packs, you will need between 1 and 7 of each. If a monthly pack has a SM card that you want to put in your SM, AM/SM, and Tau/SM decks, you will need 3 copies. If only one deck wants it (or it is Loyal), you only need 1 copy of the pack. If the pack contains neutrals, depending on how good they are, you may potentially need as many as 7 packs to have enough neutrals of that playset.

Once the first deluxe expansion comes out, this all goes nuts.

Necrons can splash any faction (except Tyranid). Once the deluxe expansion hits, if your Necron deck needs anything from Core or 1st cycle, you may have to buy extra copies of them.

ALTERNATIVE: (What I do with my LCG / CCG games so I can have multiple "ready" decks).

Prebuild your decks and sleeve them (if you are into that sort of thing). If you run into any cards that are required for multiple decks, set them to the side. Keep a printed set of decklists handy. When you want to play your SM deck, then grab it from your box, flip through the pile of "shared" cards and grab the ones your SM deck uses. Takes maybe 2 minutes to "build" the deck, since the cards are already separated. Cleanup is just pulling the "shared" cards back out and setting them aside again.

If you do this, you only need 3x Core boxes and 1x copy of each monthly cycle pack. Presumably 1x of each deluxe expansion also, but we have not seen card distribution for these yet.