One of my VPS is basically just used as a mailserver and slave DNS server and a couple of other minor things. Recently I wanted to overhaul the mailserver changing some of the software. The stuff I wanted to use was only available as 64 bit.

This got me thinking that the VPS is littered with remains of old junk data files etc from previous things as I have upgraded from Debian versions dynamically rather than fresh installs, so here was an excuse to move to 64 bit. 

Yes I know and understand the pros and cons.

I have studied various guides to doing this via the Debian web site and elsewhere and know what needs to be done, but I need a small bit of advice.

My current Kernel is linux-image-4.9.110-3+deb9u1

I plan to rsync all relevant data files (maildirectories, Bind conf files, .authorisedkeys, mysql dumps etc.) over to my home machine and redirect mail to the backup server then nuke the VPS with a complete new install of Debian stable and set up as a 64 bit install.

Does the Bitfolk self-service-network-installer coe with a 64 bit option, or do I have to install Debian stable then convert to amd64. This would still be an easy option as there would be very little software to convert/replace. I would need to install a multiarch capable kernel after using the installer (and do a second Xen retart)

If this seems a naive question sorry, we all have to learn at some time.
Thanks in advance