You need successes to heal damage with the heal skill, whereas magic requires you to spend willpower but it "just works" (misshaps notwithstanding). Note also that you can't tend to critical injuries with healing hands (but with heal skill) - you need mend wounds for that.

You roll a number of dice corresponding with the armor rating (armor + helmet). Every success removes one from the damage total. If the wearer receives any damage, then, and only then every rolled 1 in the armor roll will reduce the armor rating by 1 point.

No. If a player uses his throwing spear, let him decide which talent to use. He may switch for the next attack, but each attack should benefit from only one of the two talents.

Edit: Sorry, you basically mean can a character multiclass? No, that is not intended by the rules. I believe there's something in "reforged power" the unofficial supplement, but I would generally not allow it unless the party is 1 or 2 characters.

From his own profession, yes, absolutely.
Not at character creation though, there you can only trade one general talent for profession talent rank 2