Do you have recommended plug ings or built-in features that works well for bookkeeping
For bookkeeping? I would be very much surprised if there were. Bookkeeping is all about tables and numbers, which are the weak points of text editors. But some bookkeeping-adjacent plugins that might be helpful could be “Expression calculator” (which allows you to use the editor panel as a calculator of sorts). And the Columns++ plugin makes use of “elastic tabstops” to help present and manipulate tabular data.
What is the best way to organize and clean bank statements
I am not sure what Notepad++ brings to the “organize” space. And I am highly doubtful that there are any modern bank statements in a text format, unless maybe as JSON or XML.
working with structured data
Again, not really the strength of text editors. There are some structured data formats, like JSON and XML, that are text based, and thus fall under the purview of text editors like Notepad++. And tools like JsonTools and XML Tools help with those (but, again, often purpose-built tools are better for such data than general text editors are, even with Notepad++'s awesome plugins).
I m looking to avoid … LibreOffice for this part of my work
Avoiding tools purpose-built for the task, especially excellent free tools like LibreOffice, seems to me to be shooting onesself in one’s foot. But the plugins I’ve recommended might make certain aspects of your self-inflicted foot pain more tolerable. Good luck