1) Before people jump in and ask questions about a "Sacred Band", the term is an appropriation to describe an apparently common practice amongst the Italics, with specific references to the Samnites (And a fleeting one to the Etruscans so far). The common thread is men who participate in some sort of religious ritual that swears them to fight to the death, and hence, be a "Sacred band".
For the Samnites, the direct reference is to the "Linen Legion" or "Legio Linteata" (Linen Legion) attributed by Livy, whose name seems to either come from the place they gave their oath at (Linen roof), or from the nature of their dress, which is attributed to be bleached linen or wool and silver/tin plated bronze (as a pectoral of the goddess bust found in North Africa supports, with apparently residue of white metal plating found on it). While this Sacred band as a Linen Legion existed specifically in references of 310 and 293 by Livy, the authors Nick Sekunda & Simon Northwood argue that "the legio linteata was not a creation made just for the campaign of 293 but rather a longstanding Samnite military institution".
We see "Sacred Bands" attributed across cultures and the term seeming to be appropriated by Greek Authors as a general term for some sort of religious/holy corps of soldiers. I know you had them in Thebes, in Carthage, in Samnium, probably amongst the Etruscans and it sounds like the Gaesatae had their own religious associations. So it's not an unreasonable term.
Likewise, keeping the later attested to practice of bleached tunics and 'white metal' plated bronze is apparently due to the Samnites associating white with purity and holiness. It's doubtful that was a cultural phenomenon that manifest exclusively in the later half of the 4th century.
2) While the troops are called Oscans, which is the best available term to refer to all the South Italics be they Samnites, Lucani, Bruttii, Iapyges or whatever, they are principally meant to be Samnites ingame. The Lucani/Bruttii and Iapyges are going to be bandits that'll harass Samnite and Magna Graecia alike.
3) Hopefully it need not be addressed that the Swastika seen here is based off historical evidence, and that it was a symbol of peace or good luck in antiquity.
Stuff looks fantastic, Lynores!