LVM replication between two computers

[André Rodier <andre@rodier.me>]

Hello all,

I have a Debian Wheezy based virtualizer, with software raid properly 
configured :-)

I would like to try DRBD/GFS2 clustering, on top of an LVM, using this 
link: http://www.drbd.org/users-guide/s-lvm-lv-as-drbd-backing-dev.html

So far, the logical stack would be like this:

2 - GFS2
2 - DRBD
1 - LVM
0 - RAID1

Now, some questions:

1) At the moment, I have only one computer available, so is it possible 
to start a DRBD cluster with only one computer, and add a second 
computer later.
2) Is it really wise to use a so complex stack to host virtual machines?
3) Would it be faster to use directly LVM volumes to host virtual 
machines?
4) Would it be better to use another stack, for instance DRBD on top of 
software RAID?
5) Is DRBD is the best solution to replicate LVM modules easily with two 
computers?

My final goal is to be able to do live migration, between two or more 
virtual machines hosts, without using a shared storage.

Thanks for your advices
Andre Rodier.