Is this combination of Segmentata/Chainmail armour historical?

[Nathan Ross]

I imagine the 'padded collar' is part of the subarmalis which possibly extended up to and around the neck.

Yes, I imagined the same. We see the same on quite a few depictions. But I don't think I've seen a reconstruction of a subarmalis that does this.

the sculpture also appears to show long sleeved tunics with turned back cuffs.

Oh, I just assumed they were natty leather bracers!