Good start there Gregor.
As to painting such formations, may I suggest the following?
1) Paint it all a dark brown.
2) When that is dry, dry brush (from the top diagonally downwards) an off-white.
3) When that is dry add a FEW touches of colour.
e.g. some sleeves in a regimental colour, hats in greys & browns (go through several
units doing some hats grey, then go through again & do similar with brown.
4) Take some metallic Gel pens & tough up helmets. pike points, gun barrels etc.
Save any detailed paint work for the general