What are the sizes of model planets and the distances between them in a 50 metre garden? Is it even possible to model this without fudging the sizes? Would like to use stuff at hand such as tennis balls pea sized marbles pin heads or footballs.
Well, if I did my math right, you'd have to fudge either the sizes or the distances.
The radius if the Solar System (Sun to Neptune) is approx 4.545x10^12 meters.
Scaling that down to 50 meters, gives you a ratio of 9.09x10^10:1
The largest planet, Jupiter has a radius of 7.1492x10^7.
Scaling that down to your 50m garden would mean Jupiter has a radius of 7.865x10^-4m or 0.7865mm.
FYI I used AU for scaling. Sun-Pluto distance rounded = 40 AU so 1 AU on 50 meter scale is 1/40 x 50 = 1.25 meters or 1250 mm. Jupiter's diameter is 1.195 mm and the Sun's diameter is 11.625 mm. Saturn at 10 AU from the Sun is 12.5 meters, Jupiter at 5 AU is 6.25 meters.
Some years ago, the City of Austin made a scale model of the Solar System where Saturn, perhaps 3' in diameter and with rings, IIRC, was perhaps 7 miles from the Sun. It may or may not still exist; I couldn't find it quickly in Google. Apparently, there is something similar in Anchorage, where an attractive sphere of the Sun (yellow-- Ug) was made and plaques located to scale for the planets... here.