[qubes-users] Bringing guest OS in PVH vs. HVM

I am looking for a small footprint VM for a server, such as POP3/SMTP, or DNS. Qubes developers did a great job by providing a readily available Fedora/Debian minimal templates. It is is not clear whether their footprint is small compared to say Slackware/Gentoo.

I am exploring an opportunity to use a different Linux distribution in order to further reduce the footprint. This quest led me to the following questions.

What is a difference between bringing a guest OS in PVH vs HVM?

1) An installation of a guest OS in HVM is already covered in "Installing an OS in an HVM" section (see https://www.qubes-os.org/doc/standalone-and-hvm/#creating-an-hvm). So far, so good.

2) What about the installation of a guest OS in PVH? Is it a matter of performing (1), and then pressing a "magic button" to switch the virtualization mode from HVM to PVH? Or, is it a more elaborate process?

3) Let's assume that the guest OS is Slackware. If I understand correctly, (1) is a lighter mode of virtualization compared to (2), resulting in reduction of the memory footprint. How does one gets there? In particular, when the respective template VM is not readily available?

4) Alternatively, let's assume that the guest OS is Gentoo. Thanked to the community support, the minimal template is readily available. Where do you go form here? Does this template represent the outcome of going through all the installation steps (see Installing Gentoo chapter in https://wiki.gentoo.org/wiki/Handbook:X86#Installing_Gentoo)? And any customization of the template only requires installing additional packages? Or, further reduction of the footprint requires you to redo a subset of the installation steps, such as configuring the Linux kernel, configuring the system, and configuring the system tools?

It would be nice to hear any experience in this area.