Make maybe 4 openings of sufficient size for the water to come right out in the pot walls, where the base is met. Do not put different sized particles below the potting soil.

If anything, cover the bottom of the pot with screen or wire mesh....no nuggets or rocks, etc. And the need to add drainage holes is dependent on the size of the container. The one you describe may be adequate or you might need more. I'd lean to fewer and larger holes than lots of little ones.

Thx all. Screen/mesh was not even on my radar. I went with the 29"

https://www.crescentgarden.com/product/daniel-family-planters/

For my own wiki, what is the downside/detriment by putting a larger particulate size on the bottom.

It just reduces the volume of soil in the pot and doesn't contribute to drainage. That is because when you have a fine medium over a coarse medium, the fine medium will become saturated before releasing the water to the coarse layer.

Here's a link with a set of images that shows how water behaves when it encounters differently textured soils.

http://gardenprofessors.com/container-planting-intuition-vs-reality/

Interesting..very cut and dry per the pinks in the link. Oftentimes, I will stretch out the potting mix for the vegs in the containers. As the bark breaks down over the season, on the 2nd year, I mix in more vermic. and bark just to top off the pot. What is the effects of said pieces in a 15G pot in the similar particulate size being brought up