Donation plugin minimum amount

Hi,

Yes. In settings of the custom field you've created for the input field, you have a "regular expression" setting you can use for that.
For example, you could use the regex:

^([2-9][0-9]|\d{3,})([\.,]\d\d?)?$

Hi,;

You need to turn on the "required" setting of the custom field.
The regular expression works, I tested it, but the "required" setting has to be turned on.

Hi,

In the settings of the custom field, you have a setting "Custom Error Message" where you can enter the text you want instead.
And if you want to translate it in several languages, instead of entering the text there, enter a translation key, and then under the Languages tab of the HikaShop configuration, you can add a line in the override area for each language for that key with the text you want.