I'm in Hove, so know these roads a bit...
Avoid Worthing: It's a car park at the best of times
& if heading West Worthing to Arundel, check the jam at the West end of the dual carriageway: it's best avoided
As a rule of thumb, don't take the coast road unless you need to. Take a road one or better two in from the coast, and you can find old A & B roads that pass through quiet leafy scenery.
If you're at Powdermills you're near Rathfinney vineyard - which does a pricey coffee & snack with spectacular views :-)
Will