Easy! As long as you don't have to support IE11 or older browsers you could use <details> and <summary> natively.

No worries. The fallback for these elements is quite good. They will display as open. You won't get the open/close mechanism, but you won't lose any content either.

Almost anything you'd like. The <details> element allows all flow content, which is basically everything.

The <details> element encapsulates the <summary> element. The <summary> becomes the 'label' for the <details> and acts like a button. When clicked, the attribute open is added to the <details> element, making it display. You can therefore style the open and closed states seperately if you'd like.