Newbie Question - Ubuntu or Raspi?

Installation
1

I’m just beginning to start my Home Assistant journey and have not yet decided where to install it.
I have a number of Raspberry Pis hanging around but I also have an Ubuntu Server running Plex and backups for my family as well as running Apache2, MySQL, PHP.

Would it be best to install it on the Ubuntu Server or dedicate a Raspi to the task?

TIA

2

To start with at least, the Raspberry Pi. You can always migrate later.

Have you looked at the installation docs?