Antimagic Field Shells: not as good as you’d think
Antimagic field suppresses magic, but does not dispel or eliminate it.
An antimagic field suppresses any spell or magical effect used within, brought into, or cast into the area, but does not dispel it.
Also, from Rules Compendium pg. 11:
Spells don’t function in an antimagic area, but an antimagic area doesn’t block line of effect.
That is, magic can pass through an antimagic field, where it is suppressed and has no effect, and then emerge from the other side, where it does work. To be protected from magic by an antimagic field, you must be under the antimagic effect yourself, or it won’t work.
In addition to the rule quoted above, this interaction has been confirmed by Wizards’ customer service, and is treated as the consensus in the 3.x char-op community.
Thus, the antimagic field shell is not as good a defense as it seems at first. It does mean that melee characters are going to have a hard time (since they’ll be in the field and lose their magic gear), but by the time 7th-level spells are around, that’s not really new.
True Seeing: changes your sight, does not get projected out into an area
In the case of true seeing, that actually goes even beyond this: the effect of true seeing is on the creature granted true sight. It is a change, effectively, in their eyes, not a projection into the space being looked at (as, say, detect magic is).
Compare true seeing:
Target: Creature touched
You confer on the subject the ability to see all things as they actually are.
With detect magic:
Range: 60 ft.
Area: Cone-shaped emanation
You detect magical auras. The amount of information revealed depends on how long you study a particular area or subject. [...] If the items or creatures bearing the auras are in line of sight, you[...]
Notice that detect magic works even on things you cannot see (blocked by a fog, perhaps), while true seeing changes a creature’s vision.
Thus, so long as the one with true seeing is not inside the antimagic field itself, their true sight functions in its entirety, including the caster on the other side of the antimagic field. Even if you somehow managed to get some illusion or transmutation to work inside the antimagic field (possibly invoke magic can do that), as long as the one with true seeing isn’t in the field, their true sight functions on that too.
Detect magic, meanwhile, would fail to detect anyone standing inside an antimagic field, even if they somehow had magic with them, because detect magic itself is suppressed within the antimagic field. It would, however, work just fine on a creature on the other side of an antimagic field, such as your Selective Spell user who made it into a shell around him.