Jo Ann, coleus don't get lanky if given enough sun, food, and water. Those stuffed containers I posted above were photos taken in August. Sometimes if they start getting too tall I chop off short, stick in fresh cuttings and let them root in place.
I often have tiny plants blown out of my bloommaster pots before they're well established. I just take fresh cuttings from other coleus and poke into the soil. They grow up
Here's another August container,
How many perennials/container depends on a lot a things
Size of plant to start with
eventual size expected of plant
how long you intend to keep in the container (Years? will you leave it in the pot over winter, or transplant to garden in fall, etc)
Another option, one or two big perennial with a few smaller annuals.
Karen