Not a silly question at all! Since those are all ones that prefer to be directly sown and about now, it's different than if you were starting them in flats or something. When you direct sow, you have to allow for a good bit of loss. The packet should give you some idea of the spread rate, and you can figure from there. You don't want to spread them too thickly; thinning is a nightmare and the plants will perform and be healthier if spaced correctly. Since you have 3 kinds, i'd probably mix about a third of each pack into some sand (all together, unless you want stripes or something) and spread that as evenly as you can. If you don't get good germination in a month or so you have enough seed to try again. They all do well if sown now. I wouldn't cover them with much of anything- so make sure your bed is prepped and moderately mulched before you spread the seeds. They all need light to germinate. You can put a very thin layer of peat moss or compost on to help hold in moisture while they germinate- but you should still be able to see the seeds- no more than 1/8". Keep leaves off too. It all sounds complicated, but it really isn't. An alternative to a thin layer of peat is to take some spunbond fabric aka reemay, and lay that on top til they germinate. It helps hold in moisture and raise the temp just a few degrees but doesn't block rain or light. You can take it off once they have germinated or get to and inch or 2.

The good news is once you have these 3 going, if you let them reseed you should have them in perpetuity each year. The trick is to mulch heavily once the plants get to a decent size in spring but before they spread their seeds. If you mulch over the seeds, next year's crop won't germinate. You can always save the seed and spread it each fall, too. This method works for lots of annuals- be it summer or winter ones. Just spread the mulch before the plants set seed and you're golden.