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Here is a good 'recipe'.
5 parts perlite
4 parts bagged potting soil
1 part coarse sand
pinch of rock dust

If you purchase a cactus mix, mix this half and half with a good quality potting soil.

All succulents like a little bit of acidic addition. You can add 1 tablespoon of white vinegar to 5 gallons of water and use this to water your succulent planter.

Proper drainage is important in any container large or small.
Drainage holes are generally adequate to allow the water to freely drain from the soil and container.

A few large rocks can be used to help weight a container, if the planting may be top heavy or wind may knock over a container.

https://www.gardeningknowhow.com/special/containers/

Yes it can. I dump all the old potting soils into my wheel barrow and mash it up so it is loose again. I remove the old roots as much as possible then mix in with it about 30% new potting soils. Now I have a nice batch of ready to use potting soil at less than half the cost of the same amount bought new.

Only if the plants are already pretty well soaked and the risk of root-rot would be introduced by the rain. If you only expect a light shower or a very short period of light to medium rain, it should be fine and you won't have to water for a little while.

This article may help you:

https://www.gardeningknowhow.com/edible/vegetables/vgen/mittleider-garden-method.htm

That sounds like it could be a very interesting experiment! Keep in mind tomatoes do well in slightly acidic soil but if you use a good quality potting soil both plants will be fine. Some varieties of tomato tend to bush out quite a bit, so choose your plant carefully (Cherry tomatoes are grown quite easily in containers).
I'd be more concerned about the strawberries actually not having enough room, but go ahead and give it a try -- with the proper care, you could end up with fantastic healthy plants! Here are some articles that may also help you:

https://www.gardeningknowhow.com/edible/fruits/strawberry/growing-strawberry-plants.htm
https://www.gardeningknowhow.com/edible/vegetables/tomato/tips-for-growing-tomatoes.htm

For the Lantana, you will want to choose a pot large enough to hold its root ball with some space all the way around for growth.
For the Dahlia, you will probably want to start with a heavy pot 12" deep and 12" wide.

For more information on the care of lantanas and dahlias, please visit the following link:
https://www.gardeningknowhow.com/ornamental/flowers/lantana/lantana-plants.htm
https://www.gardeningknowhow.com/ornamental/bulbs/dahlia/tips-dahlia-planting.htm