Build 1: I have no idea how survivable pets will be when you reach high levels. It will be a LONG time for you to see an AV that is in the realm of what you read about in CoH.
One thing to keep in mind about melee vs range is that the game places higher value on melee. The reason I say that is that it is more difficult to keep a melee ally up on their feet, thus they tend to do more damage. Robots rarely engage in melee combat, so they do less damage. If you're soloing you might want something that is better enabled to take the punishment.
Build 2: so you want to be an
assholestalker

I imagine that most builds will work fine. Not sure about the survivability of SR. I like me some powersets with resistance, instead of just defense.
Build 3: AE Immobiles are great, but your targets can still fire at you. The advantage of this in a group is when corruptors get too much aggro and need to run the fuck away. If you're immobilzing, they should be able to do that much easier.