A 272 Yes.
Meeting all prerequisites at the time you take the feat is the requirement. There are no special rules about how
you meet the prerequisites. A DM who says otherwise is creating a house rule, which is outside the scope of this thread.
The Close range will restrict the available targets. As usual, you cannot target anyone unless you have line of sight to them, and cannot hit them unless you also have line of effect. There is no restriction by compass direction.
All magical effects originate at a grid intersection. If an effect is "centered on you", pick one grid intersection your character space includes. That point remains fixed relative to your character. For example, if you pick the "northeast corner" of your space, the field will continue to affect a 20' radius from your northeast corner as you move.
A 277 Ask your DM.
The game does not have rules for creating such a trap. "Attempting to cast a spell" is not a trigger in the standard trapmaking rules (either Dungeon Master's Guide
or Dungeon Master's Guide II
). The standard triggers are:
The "spell trigger" selection is only for spells like Glyph of Warding
which are traps all by themselves without any other work required.
If such a trap is to exist it must be a custom trap approved by your individual DM, who would determine all the operating parameters.