I did not mean a theme in a posh designer way, I had a friend who bought one of every plant recommended and I have to say it looked very odd. To make your garden look nice you will need something to tie it together. That could be grasses, hebes, box or lavenders. Some people choose a colour theme
too much of a novice to advise i'm just taking all the tips on board for future reference
I have very few flowers in my garden but always have colour from penstemon (deep red to lilac - mid to late summer), heuchera (black, orange, lime green - all year round) and hellebore (green, pink, white - winter) Also, grasses are excellent for giving year-long interest.
in my borders, ive gaillardias, heleniums, rudbeckia goldstrum, rudbeckia marmalade, callendula, phlox, verbena bonariensis, lithrum,sweet williams, cosmos, coreopsis, primroses ,japanese anenome,globe thistle and quite a few more, but im proud to say ive grown them all, took some doing trying to have colour in garden all year round, i dont have many bulbs in garden apart from alliums, big globe purple colouring which flowers june right next to my delphinium and campanula, ive tried one end of garden all yellow then blending oranges rushick browns then reds, pinks,blues and purples
Penstemons, fuchsias and phlox are all easy to propagate from cuttings and they all flower from June to October
I would suggest looking in other peoples gardens nearby. See what grows well in your area and you can see how big they get and whether you actually like them. If you take photos of them your garden centre or perhaps a gardener friend can tell you what they are. Look in charity shops for some gardening books too or perhaps the library. I can grow pinks and lavender in my new house but at my old house - 40 miles away - I couldn't.