Ferrus Manus is pig Latin for Iron Hand.
And that's always been rather silly, considering that later one he literally gets iron hands and then names his Legion that. I'd suggest that 'Ferrus Manus' is a title, not his name. It's something the Medusans came to call him after he defeated the Silver Wyrm and obtained his metal hands - for someone with such things might plausibly be nicknamed 'Iron Hand'. Indeed, there's an example of someone with that nickname, Colonel 'Iron Hand' Stracken of the Catachans, though as Medusa seems to have been on the feudal side I think more along the lines of 'the hero X of the Iron Hand'.
Then when the Emperor gives him a Legion, Ferrus thought that he'd extend the metaphor, for what is the X Legion but his Iron Hands? And for some reason he introduces himself to them with his title, not his name. Maybe he didn't have a name until he slew the Wyrm, and grew up alone.
In any case, I think something like that makes more sense than his name actually being
'Iron Hand' before he fought the Wyrm.
You missed Guilliman. He's actually quite interesting as he's got a pseudo-French name. One would think that Konor, his adoptive father, would have named him, and the name Guilliman doesn't make a great deal of sense against Konor's cultural background. Perhaps the vision Konor had that showed him where to find Guilliman also told him his name, or it was written on the stasis pod or something.
In any case, Guillemain is a common French surname, and there are a few historical figures with it. No one who particularly leaps out, though.
Let's see, you didn't mention Konrad Curze, whose name seems to be a Heart of Darkness
reference - to Joseph Conrad, the author, and Mr. Kurtz, the principal antagonist. Very subtle indeed.