I have a windows PC connected to Mullvad VPN and a Kali Linux VM connected to Whonix Gateway. If I start tor on the Kali to set up an .onion website..should I add another layer by connecting to a VPN on Kali as well, or is that set up anon enough? Not trying to achieve anything specific; just wondering about the level of anonymity. Thanks.
The VPN will add little to nothing and possible even harm your anonymity. There is an entire wiki written on this.
You will hear this over and over from the Tor team:
Generally speaking, we don't recommend using a VPN with Tor unless you're an advanced user who knows how to configure both in a way that doesn't compromise your privacy.