1) .000002 * 15 = .00003 km or 3 cm (I wonder if you got too many zeros in your problem? That's a really small map.)
2) I'm not sure what a chef potato is, but if the small one is geometrically similar to the big one, the ratio of the volumes is the cube of the linear ratio.
V1/V2 = (1/4)3 = 1/16
1/16 = V1/1309
V1 = 81.8 cm3
3a) Because surface area is a two dimensional measurement, the ratio of the areas is the square of the linear ratio.
a1 / a2 = 52500 / 2100 = 21 / 1
scale = √21 = 4.6
3b) V1 / V2 = 28000 / 6860 = 200 / 49
scale = 3√(200/49) = 1.6
3c) I'm not sure what you mean about the repetitive background. But based on the dimensions given:
24 / 3.5 = 6.8 or 6 vertically 42 / 2.8 = 15 horizontally
6 * 15 = 90 calendar faces