Is "Horn of Plenty" the same as "Datura"? I would separate those and plant them in the ground since they are tall and top heavy after they bloom and start setting seeds.
The rest seem to be about the same height, plus or minus a few inches.
"The Seed Site" has some seed pictures that would help ID some of your seeds. You may have to look up the botanical name of the flower to locate the correct seed image.

Here is a link that might be useful: The Seed Site

I would use the seed site to try to ID the seeds too. Then, I would separate them into individual piles and sow them separately. Why? Well, some of the seeds--like the petunias are teeny-tiny and have to be surface sown and just barely pressed into the soil. Others need to be buried under the soil.

If you plant them all together, the tiny ones will be planted too deeply for them and probably won't germinate. If you sow them all mixed together in one flat, the larger and faster growing ones will shade the smaller ones from the light.

I would separate the seeds, sow each variety in a paper cup, or six pack or whatever, and see what sprouts. Once they have their true leaves, you probably could find pictures on the internet and figure out what is what. Once you know what is what, you'll know which site in your landscape is best for each individual variety.