Are LED strips basically dimmable?

No matter what voltage the strips run on. It is not the LED that is dimmed but the power supply that operates it. Therefore, it does not matter what kind of strip you have 12/24/48/230V etc. As long as there is no additional electronics for controlling the LEDs (e.g. running lights etc.) you can give any LED strip, really any, the necessary brightness with a dimmable driver.

I can still remember the amazed looks of people in the early 2000s whenever I managed to dim any random 0815-LED, for example using a constant current source. Same here just on an ongoing basis.

Depends on the room and the furnishing.

In the kitchen, plinth lighting is suitable. In the living room and hallway, it depends on the furnishing.