Hello Ajax ..
welcome to GoY.
I've added your question to GoYpedia.
Click on gravel garden ideas and also
weed suppressing membranes
[both underlined near the gold star above]

Those will give you ideas with photos, blogs and questions, until GoYers answer your specific questions.

I hope this helps :o)

It is usual to put a membrane down and gravel on top when making this kind of garden or area, but there is a slight drawback - any planting you do will have to be through cuts in the membrane, and perennial plants, depending on what they are, need digging up and dividing periodically, and some try to spread quite a bit. It's not easy digging up a clump of something or other which is surrounded by membrane without ripping or raising more of it than you want to, so when I've planting such an area, I tend to stick to plants which don't need dividing, such as shrubs.

Also think about what chippings you use - pea shingle/gravel, for instance, is much loved by cats, who seem to think it's cat litter, so choose either larger stones, or sharp edged smaller ones. I don't know if you've got broadleaf trees nearby which may drop their leaves over your gravel, but one of my most hated jobs over the years in other people's gardens is trying to remove soggy, wet leaves in autumn from a gravel bed - without a leaf blower, it's very difficult, and even with a leaf blower, if they're really soggy, its still tedious.

As for extending the membrane beneath the raised vegetable beds, no, I'd recommend you keep those sitting on top of open soil which you've already dug over and added humus rich materials to before constructing the beds.

In the wildlife bit, can you squeeze in a hawthorn, an apple or crab apple, or a flowering cherry? All have attractive spring blossom and will support moth caterpillars, among other critters, and the hawthorn will in time be good for birds to nest in. Hawthorn and apples can be considered native, if that's important; but if it's wildlife first and native optional, think also if there's room for amelanchier lamarkii, the small birds sit and sing in mine, and the blackbirds and pigeons go mad for the fruit in late summer.