The Ghost is unaffected by the Confusion spell. While there is no strong statement that all creatures affected by a spell are "targets" of the spell, I did find this on page 205 of the PHB:

Many spells specify that a target can make a saving throw to avoid some or all of a spell's effects. The spell specifies the ability that the target use for the save and what happens on a success or failure.

This seems to imply that the targets of a spell are any creatures affected by it, although it's obviously not as clear as we could hope. Another example, on page 196:

If a spell or other effect deals damage to more than one target at the same time, roll the damage once for all of them. For example, when a wizard casts fireball or a cleric casts flame strike, the spell's damage is rolled once for all creatures caught in the blast.

As backup for this, we have the Ghost's Possession ability on page 147 of the Monster Manual:

The ghost can't be targeted by any attack, spell, or other effect, except ones that turn undead[...].

Turn Undead is an AOE ability, not a targeted one. If the Ghost was still meant to be affected by AOE spells and abilities, the caveat for Turn Undead would not be necessary.

And finally, if AOE spells did affect a Ghost in the midst of possessing someone, the Ghost would be affected by every Fireball or Lightning Bolt that hit the possessed creature. In your fourth point, you asserted that this obviously wasn't the case, which I agree with. There's no reason why Confusion would work differently than every other AOE spell.

Both Misty Step and Dimension Door work unimpeded

Misty Step and Dimension Door, when cast on creature outside the barrier, do not affect or target creatures or objects within the barrier, and they don't affect an area. Furthermore, Globe of Invulnerability does not block vision (required for Misty Step), nor does it prevent targeting of points within it (required for Dimension Door). So it seems that nothing in the text of Globe of Invulnerability would interfere with either of these spells.

Other teleportation spells might be affected

Note that while the two specific spells in the question are not blocked, not every teleportation spell is guaranteed to get through. For example, suppose you cast Steel Wind Strike targeting only creatures within the globe. The relevant parts of the spell's text are:

[...] Make a melee spell attack against each target. [...] You can then teleport to an unoccupied space you can see within 5 feet of one of the targets you hit or missed.

If all targets are unaffected due to the protection of the globe, then you have not hit or missed any of them, because you have not attacked them. Therefore, you cannot teleport using the spell, since you have no valid targets to teleport next to.

So, it's important to read the text of the specific spell you want to use to determine what interaction it will have with Globe of Invulnerability.