A US faction in Holdfast may seem really far fetched, but in reality it isn't really that crazy of an idea. (and all of this is just my personal opinion for the regiments chosen)
Context (Read if you want to know why I suggested this):Classes
Officer: (On the left) Standard officer from most regiments (on the right) a Colonel .
1st Line Infantry(& Flag Bearer): A soldier from the 25th Infantry with a flag bearer.
2nd Line Infantry Variant: A soldier from the 22nd Infantry.
3rd Line Infantry Variant (if it ever gets added): A soldier from either the 1st or the 7th
NCO: Any infantryman variant with an added red silk sash belt and epaulets
Light Infantry: Rifleman from the 4th Infantry or an infantryman from the 17th
Rifleman: Rifleman from the 1st Regiment of Rifles.
Surgeon: A NCO with a tailcoat, top hat, gaiters, and glasses.
Sapper(Carpenter): A pioneer from the 25th
Drummer/Fifer: Musicians from the 25th (Would've had white trousers)
Grenadier: Infantrymen but with chevrons and red tips on their plumes
Cavalry: 2nd Regiment of Light DragoonsFife & Drum Tunes:
Yankee Doodle Dandy
The Roving Sailor
March to Boston
Downfall of Paris
I might do a naval one soon, feel free to add on or ask any questions.