That will work. Personally I would rather have one $20.00 plant than four $5.00 plants. Part of that is because I am 69 and digging up those plants next year would not thrill me.
Throw out a mix of annual seeds until for a couple of years until your perennials take off.
My best fillers for spring are larkspur and poppies. (plant early fall). For now a lot of zinnias. When they go to seed scatter those back into the same bed.

I'm still in fairly good shape and when it gets too much I have 18 & 19 year boys that are a big help . I also have 8 acres of land so there is always a spot to move things to . I had put down some Preen when I started because we were also seeding the lawn and I didn't want grass growing up in the bed - I figured seeds probably wont germinate due to that . Thanks for the advice .

I prefer to give plants their final spacing and then plant annuals or place potted plants in between. If you start plants from seed in pots, and then plant in the beds, the Preen won't effect them since it works on seeds to prevent germination. I find each time I transplant, it sets things back a bit and I'd rather spend the time and energy doing something other than transplanting.

Just make certain you don't plant any permanents (like shrubs and trees) too close. the others you can deal with. It is your garden, so you get to plant it to suit yourself.
kay