I'd go over the top of old benchtop....a good stone mason should be able to cut and glue edges on the sides so you won't see the old bench underneath.

Nice sandstone windowsills....I'd be making them a feature. You said no grey, why?. It would be perfect here, look great with your white gutters/downpipes and really set off…

Depends on your budget....I'd look at getting rid of aluminium windows for some timber window frames, and a nice entry door set. Maybe ebay for 2nd hand stuff?. …