Best type of shower

Limescale isn't good for any shower however it is easier to manage on mixer showers. Electric showers have heating elements inside of them which after some time get scaled up and break. You would need to make sure that you have fairly equal pressures for the mixer shower rather than an electric shower that only needs cable and a cold main feed.

There's no correct answer here apart from i would strongly recommend that you have a limescale inhibitor installed on your mains water as it enters the building (generally under stairs). You can also have a water softener installed, again have it installed on the mains water pipe before it tee's off for boiler or bathroom. Hope this helps

Yeah agree with the above filter the incoming supply to alleviate the problem.

An electric shower is ideal when multiple showers are needed and a hot water cylinder could well run cold. Electric showers just like kettles can get scaled up so fitting a descaling device in the supply pipe can help , they are easy to change too. A mixer shower is best when there is no shortage of hot water and also when a forceful shower is preferred as a booster pump can be included. Again fit a descaling device to the rising main to cut down on scale.