Cloaked Figure wrote:
He's too old to use for humans, since the starting age is 20. But he doesn't quite fit any other race. Or does he?
I wouldn't be too hasty with throwing the old man out. A character in Arcanum always starts with the age which is just after the thresholdof gaining maturity in every race. Now let's look at a few examples:

Do any of the portraits look like a fresh adult? Definitely no. Do they fit Arcanum? Hell yes. I'd say that the beginning age can be ignored in quite a lot of cases. It should be made Fallout style.
Cloaked Figure wrote:
I've also been wondering whether or not I should edit the new portraits' backgrounds to make them light blue like the original Arcanum portraits. It might hurt the quality of the portrait, or clip off parts of the face, which I don't wanna do.
Look through all of the Arcanum portraits. Not all of them all blue. Some are white, some are yellow, some are green. The rule seems to be the background being light and homogeneous (maybe also it being a cold color, but that depends on interpretation). As long as these requirements are met, everything fits the scheme.
Cloaked Figure wrote:
Edit: I'm also considering pulling Churchill's portrait out of the mod, since it breaks immersion to have a famous person as a selectable portrait.
The man here is Ambrose Burnside, a XIXth century American general (or at least a less bold version of him), while the woman is a member of the Troika staff. Does knowing this make the experience of having a character with their face in any way disturbed? I think not. In some cases it can even add some flavour.