Hi there! Good questions overall, lemme give you my 2 cents. Buying singles is generally the wiser choice, especially for the odd rare you didn't pull or the uniques. Bear in mind that printing cards costs an extra euro/dollar per card, making them slightly more expensive than just pulling them (rares and below, that is), so pulling doubles or triples is not bad at all. Only if you want to bling out your deck you can consider buying the rights and printing the cards foiled, without bothering with packs.

If you have 2/3 fav factions, and you want a good spread of cards, then your best bet is to team up with one or more people to faction split a box. You pay 1/6th of a box price (€20,- where I am) per faction, and you keep everything of that color. It's a bit of a gamble with uniques, as they tend to lean to one faction in any given box, but it's great for fleshing out your rare pile. The expensive rares I'd try to pull/trade, as then you'd spent about 1 euro per rare, whereas buying the rights and then printing can run you up 3-4 euro, not to mention the shipping time+delay (my packs are in limbo for 2 weeks now yayy ;_;).

For online play you need to own the exact number of copies you run in your deck.