Hi Ben,
The goods run round, or goods loop, is the magenta one (on a tweaked version of your plan):
The goods train would run directly into the goods loop or possibly into the platform if it was empty. The signalling should allow either type of arrival so that goods trains can arrive and be dealt with when there are passenger trains in the station or vice versa.
It would then get shunted from there into various sidings (the brake van probably being left in the spur at the end of the middle road, the release road, while that's going on).
You can probably see why I suggested lengthening it. In that location it shares the release line with the platform and because it would get freed up quite quickly it doesn't get in the way of access to the shed too much. (Lambourn had a similar arrangement.)
You might need to give the cattle dock more room in that position but it's quite hidden in that back corner and you could instead make it low relief. Perhaps just show the front fencing with some overhanging foliage to disguise the lack of a back.
I'm thinking that there is only one passenger platform side. The goods shed side of the platform would have a fence along it. (See Moretonhampstead.) Two passenger platforms in a little station like this would be very unusual unless it was very busy for some reason. Model BLTs often have more platform capacity than reality, admittedly, but you're fighting for space here and something's got to give!
There is just about space for a short extra goods siding, shown in cyan above. That gives you a bit more capacity while still allowing good vehicle access to the yard and the back of the shed.
P.S. I am GWR biased but I think these basic principles apply whatever company you're modelling. It would be worth checking with an SR expert, though.
P.P.S. Wallingford is a good example of a private industry siding (a dairy) kicking back off the main line just outside the station. Milk tankers were brought in with the goods train and then worked back up the line to the dairy.