So far I have:
Purchased 5 new roses (2 floribundas, 2 hybrid musks and a polyantha)
Purchased a variety of plants to fill in around the roses (Missouri Evening Primrose, various Columbines, 2 varieties of Coreopsis, an annual I've been wanting to try called Cleome, a couple of random Dahlias to try in ground, seeds for Baby's Breath, seeds for Vulcan and Zebrina Mallow)
Had the new strip tilled, it was just regular lawn (not grass just weeds)
Amended the new strip, plus in between the existing roses
Watered in the amendments and shaped the new bed to get ready for edging
Purchased enough mulch for at least 2 inches covering the entire area
Purchased edging to match the next door shade bed
Tomorrow I will lay out the plants and I plan to plant thursday and friday

Anything obvious I'm missing? Any recommendations for other steps or tips for success. I've been planning and dreaming all winter and don't want to mess this up.

Evening primrose tends to spread--a LOT--where I am. I've pulled it out for years and this year it's back with a vengeance.

I have stokesia/Stoke's aster & Penstemon/beardtongue 'Mystica' in both my full-sun and part-sun beds. They're both reliable and I've noticed neither requires any attention from me (always a plus). Another low/no-care perennial, Sedum 'Blackjack' would add some textural contrast. Platycodon grandiflora/balloon flower is also an easy, zero-care, reliable full-sun perennial. The species flower is blue but there are also white, pale pink & double-flowered cultivars available.

Good luck!

Here's a few that I'm putting in that I got from Lazy S's

Helenium autumnale
Perovskia
Solidago "Fireworks" (shorter than species)
Phlox paniculata "Alexander" but there are hundreds of varieties
Salvia azurea (lots of different Salvias)
Nepetea Clarkii (or Walker's low)
Eryngium
Guara Lindheimerii
Coreopsis (lots of varieties)

Not so bad with the roses at the back.

I had a problem with cleome reseeding around perennial beds.

Woody included pictures of some too quite recently.

Very interesting to see/read before and after garden pictures/info.

As said, I have had cleome, which was used as an annual filler, reseeding in mixed perennial beds. A problem (in that particular case) was the reseeded plants were too scattered.

On the other hand, I'd say cleome is a very attractive annual. The whole plant is elegant and I do think that it can compliment perennials.

I have started clipping off the lower seed pods every couple of weeks. I ask one of my kids to help and they hold a container while I snip them off.

You can let some seed pods ripen and collect the seed for next year.