It's beautiful @Chumley
! And time is indeed a gardener's friend - give it a few years and you'll be dividing and looking for places to move plants. The old saying about perennials is "the first year they sleep, the second year they creep, the third year they leap". We have found that to be very true. The other one that you rarely hear is "fifty percent of everything you plant will probably die the first year" but that's another story!
The hostas may prove difficult - they generally prefer at least some shade and your pond appears to be in full sun... but maybe I'm not seeing the whole picture. And having said that, I have a lot of my own planted in the sun. They do fine until the very hottest part of summer. If you do find them unhappy where they are, you could move them into the actual stream bed - I have some planted in my waterfall that look great all summer. The constant water supply counteracts the lack of shade and keeps them happy.
I also think you have to consider adding some annuals every year. Perennials are great, but most only flower for short periods each season. If you want to add all season color, you can't beat annuals. A few tucked here and there can have a great impact and are really a small investment.
I also love a few pieces of garden art - a gazing ball or other colorful glass ornaments can add some nice colorful accents. And pieces that move with the wind are also fun to have - I've seen some really interesting metal or copper pieces at local nurseries that have colorful beads or shiny pieces that catch the light when they spin or bob and weave with the wind. I like a little whimsy in the garden spaces - it's eye catching and fun!