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The garage should be warm enough for a day or so. It will have stored its own heat that will keep it warmer than the outside.

These artilces will help: https://www.gardeningknowhow.com/plant-problems/environmental/protect-plants-in-freeze.htm
https://www.gardeningknowhow.com/plant-problems/environmental/frost-how-to-protect-your-plants.htm

Yes, placing a berm in the landscape can redirect drainage and reduce flooding. These articles will help:
https://www.gardeningknowhow.com/special/spaces/building-a-berm-how-do-i-make-a-berm.htm
https://www.gardeningknowhow.com/special/spaces/creating-and-using-berms-in-the-landscape.htm

If they are in containers, you can easily move them to a shadier location. Unless you acclimate them, they may suffer from stress in the basement, going from one extreme to another, but if the temps are reasonably close to what they normally receive outdoors, this should be okay. You can also get some shade cloth for plants that cannot be moved. Also, make sure they are receiving plenty of water during heat waves/drought.

Perhaps, some of the suggestions in these articles will help you: https://www.gardeningknowhow.com/ornamental/flowers/fgen/full-sun-plants.htm
https://www.gardeningknowhow.com/special/xeriscape/drought-tolerant-flowers.htm

Grass naturally goes dormant when the weather gets dry. All you need to do to bring it back to green is to water it regularly. make sure it gets 2-3" of water a week.

Even if you do not water it, it will come back when its starts to rain more, whether that be this year or next.