[RPG] Which school of magic do magical weapons and armor auras radiate

Since all of the Detect spells have a duration of Concentration, it seems to me like you have to concentrate to gain a benefit from them. If the Night Hag concentrates for 1 round, she can use any of her detect spells without having to cast it, but she doesn't get any information without concentrating. The difference here between continuous and at will is that the continuous version doesn't provoke an attack of opportunity. I don't think there's a solid rule on this, but I feel like this solution fits the normal behavior of the spells best.

When special abilities modify the enhancement bonus, you use the total enhancement bonus to determine cost. This applies to weapons, armor and shields.

Special abilities count as additional bonuses for determining the market value of the item, but do not modify attack or damage bonuses (except where specifically noted). A single weapon cannot have a modified bonus (enhancement bonus plus special ability bonus equivalents) higher than +10.

Your example of a +1 Flaming weapon has a +2 enhancement bonus and thus costs 8000g + base item and masterworking.

Some qualities from outside of the SRD have direct cost modifiers like +300gp. These just add on to the price instead of changing the enhancement bonus.