Forgiving the current topic of Hand of Bim Shalla, 6x of anything is usually excessive, and by no means vital to be competitive. Generally you only need 2-3 copies of your important cards, in some cases only 1-2.
As far as building a competitive set, I do think you need more than whats in one base set.
Ideally, I prefer 2x core sets up front. You then have double the allotment of cards, but you also get another set of status boards, mage cards, damage dice, tokens and counters which makes it tons easier to have 4 player games.
From the two sets you can take a look at what you have to work with. For one person you should have a decent stock of basics, and youll have 2 of all the mid to higher level stuff (youll only get 1 necropian vampiress, or staff of asyra per set or tome for example) But, by and large you can get away with running no more than 2 copies of a lot of those spells too. If you find you are sorely lacking or just HAVE to have some more of the base set, then look into what each tome contains and pick them up on an as needed basis, or might be able to luck out and find a singles dealer (ive heard they are out there, but never seen it.)
The good news is that after that, Arcane Wonders got really generous with their sets. Forcemaster vs Warlord comes with 4-6 copies of all its bulk spells and 2 of all the legendary stuff.. so you only really need to buy it one time ever. Conquest is done on the same model I believe. So once you get caught up in the core stuff, moving forward its going to be tons easier of only needing to pick up one time expansions every so many months.
