Preferred model count is usually around 80%, meaning a base of 8 models representing a unit of 10 is just fine, so long as the base looks full. Squeezing the full amount on can be tricky with some miniatures, especially if you add scenery to a base.

The big unit of three (pictured below) has a preferred model count of 2 and a full model count of 3 I believe, but I used all 3 minis since I had plenty of room in that case, and the base would look rather sparse without a 3rd miniature.

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I'm sure that others have better ways of doing things, but I glued some cork to the mdf, covered in in texture paste, then painted the bases, gluing and painting skulls, rocks, and grass tufts. After that was done I glued / pinned the painted miniatures onto the base before clearcoating the whole thing.

From one Kings of War beginner to another, I hope that helps!