How to create a new wordpress with existing domain w/o interrupting current site

Hello,
sorry in advance if I sound clueless and my questions are ridiculous.

We have a company website, built with wordpress.
Many developers have worked/coded on it and it has gotten very messy and slow.
We want to build a new site with wordpress and when that is ready, we want to give it our existing domain.

How do I do that!?

Do I open a wordpress account and buy a random domain name until I build it and then transfer it? Or can I rebuilt my site from scratch using the same wordpress account?

Any leads on this process are much appreciated. Thanks!!