You could use some john innes , but i use my own compost/leafmould chuck some grit in so that its free draining and this will work well for you, flowering alpines i cut the spent flowers back, and reduce the clump size if it gets a large spread.

As above, lots of grit in the soil...alpines hate sitting in cold, wet soil.

As for cutting back, many "alpines" such as aubretia, alyssum, arabis, saponaria and some veronicas....the ones that spread and creep, would usually benefit from a light trim after flowering. Mound forming ones such as saxifragas and small dianthus just need dead heading.

Just to clear things up....the term "alpine" is very loosely applied these days. Low growing perennials such as aubretia, saponaria, iberis and erodiums are not really true alpines. They do look good though !!!!

Soil and grit with some humus material. I do not use composts or fertilisers in the alpine garden because, in nature, these plants grow in very thin, poor soils.

As mentioned before lots of grit to make a very free draining compost. I believe the 'enemy' of alpines is not the cold but the wet during winter. You don't need an alpine garden as such but a few, round pans, filled with good compost and grit and planted with choice alpines in a cold greenhouse should be a worth while planting scheme.
I live near the Cambridge Botanical Garden and they have a wonderful alpine house. It makes a glorious site.

I like the greenhouse idea john. And thanks guys for all your help .