Where are you in UK, John?

Sedum, crocosmia, helianthemum, eryngium, some hardy geraniums but not all, euphorbia, delosperma (especially)

Some windbreak would help too, perhaps sea buckthorn or even eleagnus. Rosa Rugosa would make a good 3-4foot hedge with great flowers and red hips and does well right on the coast. Hydrangeas might be OK if its not too dry as they usually do well be the sea. Give them lots of compost though.

Snap! I have the same conditions. I'd add Libertia, hardy fuchsias, pinks, lavender (the tough ones, not French lavender), penstemons.

One trick I use when planting on a steep hillside is to crowbar a planting hole that is a bit bigger and deeper than you need, taking out the stones you come across and putting them at the front to make a little wall that forms a "balcony". Add compost, water retaining gel crystals and slow release fertilizer granules to the soil at the bottom of the hole, mixing it in well with what's there already. Plant your plant, making sure that it is on a little shelf of level soil (that's where the "balcony" comes in) so that when it rains, or you water it, there is more chance of the water soaking in where your plant is.

When I'm planting on a really steep hillside I don't worry overmuch about getting the tall stuff at the back and the low growers at the front - I see them like the audience in a steeply banked theatre, so everyone gets a good view - and we can see all the plants. It can look really spectacular - good luck.