That's just a small part of my garden
Much of it is rock and alpine plants, but there are other borders. Then there's the veg patch. I suppose nowadays the gardens are my chief joy
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The pics were taken a year apart, so were 2 or 3 years old. The first year everything looks very sparse, but the second year it will already be making an impact if you place the plants quite densely.
Most of the herbaceous perennials I've mentioned are quite common, propagate readily from seeds and cuttings, are hardy here in Scotland, smell good and are loved by bees and some by butterflies. I've marked the ones the bees are especially fond of, but the only flowers bees don't like are the double kind because they can't get in, and pollen free cultivars developed for hay fever sufferers.
For suppliers, either go to a large garden centre several times in a year, beg cuttings from friends, grow from seeds, or explore online specialist nurseries (I can't think of any at this time of night). Most of the online nurseries I like are for alpines, although they often have many varieties of thymes. Just google 'hardy perennial nurseries' either near you, or anywhere for mail order. You can pick up good plants at plant sales and shows (Carlisle Rare Breeds sale used to have plant stalls, RHS does)
With that kind of garden you don't plant it up all in one go. I had a very basic plan then I started sticking plants in as I bought them. As time has gone on I've found that many plants are in the wrong place or far too big, so I either move them (in the winter) or give them to someone else. I don't think you need a careful plan for a cottage garden. I buy a plant then find a gap for it. The low herbs, pinks, sempervivums, low campanulas and so on are more visible if they are near a path.
For the bed in the picture, I have a path through the middle. It was built straight, but I have planted spreading, cushiony plants at the edges in such a way that it winds through the beds. I think that would work with yours, as it's quite wide.
I use very few annuals as they are difficult to place, apart from rudbeckias. Spring is dominated by bulbs - daffodils, crocus, tulips, snowdrops, aconites, which die down before the main plants are up. For bulbs, plant them in groups of 5 to 9 of the same variety as they look far more effective.
For learning which plants are which, look online, then haunt the garden centres. ID books never seem to quite have what you want to look up