So I'm building around 70 VMs this week via Foreman, and for each one, what I do is this:

0. Get it to boot + install
1. Shut it off
2. Make it auto-start on boot via virt-manager
3. Turn on the boot menu via virt-manager
4. Make HDD the first option via virt-manager
5. Switch the primary disk from virtio to scsi via virt-manager (which changes the disk type and adds the SCSI controller)
6. Edit the XML manually via virsh -c qemu+ssh://(host)/system edit (host) to:
a. Add <memoryBacking><hugepages/></memoryBacking>, since all our KVM hosts have 75% of RAM dedicated to hugetlbfs
b. Add <cpu model='host-passthrough'/>, since they're all hosted locally, and we're never going to migrate
c. Add model='virtio-scsi' to the SCSI controller added in #2
7. Restart

It would be nice to have some kind of GUI for these things:

1. Ability to autostart on boot, per-host
2. Auto-detect the presence of hugepages (I don't think this is possible with libvirt as it exists today), or allow a checkbox on a per-CR / per-guest basis to use hugepages
3. CPU types dropdown, based on the result of the "virsh capabilities" command, albeit with a "Passthrough (no migration)" option
4. Disk type selection---by default, with CentOS/RHEL6.3+, you probably want virtio-scsi; with RH < 6.3 or Fedora < 17, you want virtio, with Windows you want something else, etc.)

I'd say just display the boot menu all the time, personally.