Thanks Doc! I do need to work on more bandits and peasants.
I'd also say now that I've done 'em that you can probably use pretty much any unbearded head for Sohei with cowls. Go through your parts box for ones with really ugly hair but okay faces if you want to convert your own (though it would still be best to roughly round off the skull... Fuzzy Wuzzy heads might be asking a bit much...)
Its the remnants of sand used for basing pavers that I got out from my garden at our previous house about 15 years ago. There's a bit of dirt in with it as a result. I half filled up an ice-cream container with it and have been using as my base dipping ever since.
Unless you're going for a rocky look, I find smaller particles are best.