OK, stand by - here comes the cold water ...

You absolutely must have drainage holes - putting things in the bottom of the pot doesn't do the same job.

The size you quote is too small for three lots of healthy herb plants. I'd give each one a 12 inch diameter pot.

Basil does not want the same conditions as parsley and cilantro (less water and more sun).

Parsley has a long tap root and dislikes being transplanted.

Cilantro is a fast growing annual which is likely to bolt if transplanted.You need to sow in clusters and keep sowing every few weeks.

If you want to grow all three herbs together you could try sowing each one into its own container and then gathering the containers into a single cache pot. Then you can water them individually.

lol at the cold water comment! Thanks for the advice!

Why do all plant pots not come with drainage holes if it is a must??

I also want to grow rosemary, thyme, mint and spinach. I know mint needs to grow in its own space and you said above that basil needs different conditions than parsley and cilantro. I don't know how spinach grows. Between all of the things I want to grow, what can I put in the same pot?

Personally I'd give each plant its own pot. It may be less aesthetically pleasing to you but from your plants' point of view it's the best thing.

Spinach cooks down massively so you need a lot of it. A shopping bag full of leaves gives about two portions of cooked vegetable. You might find Swiss chard an easier substitute vegetable. But you still need a good quantity.

Rosemary is a shrub and needs a large pot of its own. Since we don't know where you live we can't tell you if it will live through the winter for you.

Thyme is a sub-shrub and also needs its own space. It needs far less water than parsley, mint, cilantro or spinach. As does Rosemary.

I don't know why pots are sold without drainage. Maybe they're intended as cache pots or maybe the buyer is meant to make their own holes. Or maybe the makers just don't care....