Recent dicussion on the type of database to use,
https://coderanch.com/t/622939/jforum/Mild-warning-suggestion-develop-Oracle
Upshot: HSQLDB is marvellous for a trial, as you need nothing installed, barely any
Java setup at all (not words you will hear too often). But is not recommended for production.
I do appreciate the trouble in setting up a database, from scratch, for non-professionals and others without help behind them, I do. It's a grind. But if you feel from the start you will be using JForum, you may as well do it now. JForum can work with any DB having Java connectors, (Derby, Postgre, MySQL...). I really recommend biting the bullet and finding instructions for your OS and environment. Do the job thoroughly, because JForum has both an installer, and it's manual setup through proprty files is about as good as it gets.
Extra thouught - if you have no overwhelming inclination towards one database or another, consider how you might be deploying the forum. I know it's a long way in the future, but consider which databases are are supported by the deployment method. Otherwise, you might wind up having to migrate data from one DB to anotther...
Rob