Speaking as the guy who often gets called because "we had our hardscaping done by this great guy but he doesn't do plants and we have no idea what to put here" - come on, man, give me something to work with. My rule of thumb for keeping it stupid simple: unless there is a darn good reason, don't do a plant bed less than 5'. If the planting bed is behind a wall, 6-8' minimum. Trust me.
What would've made a huge difference would be if you had opened that radius way up and come farther out into the yard. Honestly, something with a 10' radius or so wouldn't have been a lot more costly, you could have then had a nice bed with a rockin' ornamental tree to anchor it, and it would've tied the whole project together better.