Answer: I don't see why you couldn't plant the seeds directly in the containers and achieve good results. With regard to rules of thumb, the one difference I can think of is that the soil temperature may fluctuate a bit more than it would in the ground and that you will have to be extra careful about keeping an eye on the moisture because the container mix is likely to dry out faster than the ground would, especially on warm or windy days.
Once the seeds germinate, you can thin as needed and even transplant the seedlings to get the spacing you want.
Have fun with your project!
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