Quick pic of progress made today, the glue on the track centres and immediate edges is now dry, so I've been gradually layering up the ballast in the area between tracks. 

The method is pretty simple:

1. Wet baseboard area to be ballasted with very weak Copydex-water-washing up liquid solution.

2. Sprinkle on sand.

3. Drip stronger (1-4) glue solution over sand.

4. Repeat steps 2 and 3.

The glue is still wet in these pictures: 

As you can see, I don't really mind having some ballast on the sleepers - I'm taking inspiration from local examples with regards to this and the colouration that I'm trying to achieve:

Thank you for looking in!