You can buy ONE card unless you have a card in hand with the Fortune symbol (page 21). You CAN chain these together as long as you have enough Clarity to keep buying.
The main rules clearly state this, yes, but then the FAQ (#21) explicitly states that they do NOT chain, and you can never have more than two total buys. My guess is that the FAQ is wrong.
Page 23 of the instructions state "When [an artifact] appears in the player's hand in the course of normal play, it can be equipped immediately into the player's Regalia Zone, and its effects occur instantly." I interpret that to mean that YES - you can equip it before any Miasma effects fire off.
No, because Miasma fires off during the beginning phase, and equipping of artifacts happens during the action phase. (Page 17: (2)(a) "Artifacts can enter the Regalia Zone and have an effect".)