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For outside, this can be quite difficult. You need plenty of dolomitic lime, wettable sulfur, and organic slow release feeds of your choice, since they will all be constantly washed out. You also need meters to test for soil pH, and EC (electrical conductivity) which will tell you how much nutrients are still in the soil.

You containers need to be VERY large and have plenty of drainage. Your size will depend on the plant in question, but generally a 15 gallon will grow anything that you need, foodwise. Paint them white for protection from heat.

This is a 'learn as you go' thing, and will require years of practice in container to nail it down. This method is worth the trouble if you have no other options, though.

You will want to plant them in a plastic pot that keeps the roots from touching the paint or metal. Depending on the type of metal, it can be toxic to the plant. The same goes for the type of paint. They are meant to house a container of a similar size as a decorative shell.

As far as what to plant... It is very difficult to get a size reference from a photo, but there are things that will grow in small containers, such as strawberries, miniature tomatoes (like the Tiny Tom variety) basil, and many other small herbs.

It depends on the plant. Many plants like to be repotted, once or twice per year, and many don't like to be moved ever once established. It is very plant specific.

These articles will help:

https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm

https://www.gardeningknowhow.com/houseplants/hpgen/repotting-a-large-plant.htm

https://www.gardeningknowhow.com/houseplants/hpgen/should-you-repot-your-plant-happy-root-bound-house-plants.htm

You will want to plant into a rich potting soil. There will be no need to mix extra nutrients, as transplanting will be quite hard on the plant. This means that it will not take up nutrients for a short while after transplant. If there is too much nutrients in the soil at this time, then you risk burning new roots and killing off the plants.

Your best option is a container only a few inches bigger on each side, and nothing too much bigger. This will make the problem worse. If you wish to put them back into the same container, then make sure to treat for infection with a fungicide prior to replanting.

This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

You will have to have multiple people help lift and pull in order to save the container.

This article will help you to repot a large plant: https://www.gardeningknowhow.com/houseplants/hpgen/repotting-a-large-plant.htm

You are very limited in what will grow in these conditions. I'm not very familiar with the climate in your country, so you could be limited by that as well.

This article will help you to grow small container water gardens, which will apply to your situation, as well as offer some suggestions on what you can plant: https://www.gardeningknowhow.com/ornamental/water-plants/wgen/patio-water-gardens-and-plants.htm

There is no certain amount or diameter of the hole. Just be sure that they are a few cm apart from each other. The potting mix should be light and provide most of the drainage. The holes will allow water to flow out of the container. With the right mix, as little as two holes will allow for proper drainage, although I would recommend more than that. Some containers I see have their holes not on the bottom of the pot, but on the lower sides. This helps facilitate drainage in my opinion.
https://www.gardeningknowhow.com/garden-how-to/propagation/propgen/containers-for-propagating.htm