You can do this as easily as using different sys-firewalls for groups of
qubes, or indeed using different sys-net routes.
You should think carefully about why you want to do this - if you
genuinely want to separate out your online activities, then you probably
want to have (at least) 2 sys-net qubes using alternative routes to the
net - don’t connect them to the same router and don’t connect them to the
same power supply. Using a burner mobile connection would be good.
Set up your sys-net/sys-firewall pairings and assign qube groups to
them.
Use multiple templates, differently configured.
Have a vanilla qube and use it heavily for normal use - I mean what
other users will do, unconnected to your other activities. You can
script this if you will.
Use different VPN suppliers and/or accounts: Just set up a VPN gateway
on each line, or use different gateways.
Consider using a VPN client installed in each qube.
Be consistent in your usage and don’t be tempted (for whatever reason)
to switch a qube from one group to the other.
Don’t mix usage after you have set up the qubes in their groups: guard
against accidental use. Anything you can do to help enforce this would
be good. Have multiple desktops. Colour code them. Force qubes to
appear on the relevant desktops. (Switch to KDE, and use Activities to
make this simple.)
As to the use of VPNs, be careful what you choose and don’t trust anyone
who says they don’t log. Experience shows this is rarely true.
Payment may be an issue, and an identifying vector.
If your profile is such that this really matters to you, then I would
use multiple VPN accounts and providers, and change frequently.
You WILL have identifying habits - you need to break them: don’t let
your use of infrastructure become another identifying feature.