Welcome to OpenStreetMap and thanks for adding some much needed detail in Shenfield.

I hope the following are useful. They're not intended as a criticism - after 6 years I'm still finding new or better ways to tag objects on the map.

For residential gardens, rather than using natural=grassland, you can use the tagging combination

leisure=garden + garden:type=residential + access=private

The documentation on leisure=garden is at https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dgarden

When you add private outdoor swimming pools, leisure=swimming_pool is quite correct, but it's worth adding access=private and location=outdoor.
https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dswimming_pool