Am I wrong, or is it not possible to create your own enemy contacts...I have to use the pre-generated ones.

You can create a custom appearance, but the actual NPCs have to be one of the existing factions. So pick which enemy group has the type of attacks you want your enemies to have, and then place a spawn of that group and give them all the custom costume you created.

Per usual, you are there with helpful tips, and for that I thank you. Another question for you. Can you get an npc to follow you through a mission?

Not directly. You can create wandering friendly NPCs and might be able to string one or more along by spawning enemies along a path close enough to pick fights with them and drag them forward.

Having the option of having a NPC follow you would be awesome! You could assign him the same tech as a BOFF - or even replace a BOFF with a custom NPC. Which brings me again to the away team limit option.

Also, when speaking about giving NPC groups a costume: It would be great, if you could assign a costume to an entire group and have the game randomize only race, gender and head.