A summary of questions for a rules-freak

[Ducallan]

To add to emigio's answer:

You can sell on your turn when not in combat, and before you start the charity phase.

If you're talking about the original Hirelings cards (treasure cards), they are basically a cheat card, so you they can carry any one item for you, allowing you to ignore the size, race, class, sex, or slot requirements on that card. Door card Hirelings from expansion sets can only carry what their text specifically says, and are subject to race/class/sex item restrictions: they are only what class *or* race their name says, regardless of what they look like; their sex is what they look like (the Gnome Hireling is male, which isn't clear from the picture).

The 'payment' for taking from the discard pile occurs after the card is taken, but the payment happens from your hand *before* you can possibly take it into your hand so you can't pay with the card you just drew. Also remember that the card is treated the same as if it were drawn normally: if this was during 'kicking down the door', you only take it into your hand if it wasn't a monster or a curse. You fight it if it was a monster, and you get cursed if it was a curse.

The Doppelganger card is an item that gives you a bonus equal to your current strength. You always calculate your strength without the card, then double it. It updates with each and every change to your strength.