I have now performed a number of installations using several partitions, i.e. separate /boot, /usr ... and so on.

A couple of notes about MBR setup:

1) a separate /boot is allowed and supported from pc-sysinstall, in which case it must be the first partition, this is a pc-sysinstall requirement.

2) a separate /etc is allowed and works. provided it is defined after '/' fs.
Requesting first /etc and immediately after '/' filesystem cause pc-sysinstall to loop continuously around 'parseconfig.sh' - reason unknown and most likely we don't need to know about, because we will enforce '/' as the first partition.

3) there is no requiremnt for SWAP to be in a specific position, in fact the layout below worked quite fine:
/ + /tmp + /usr + /var + SWAP

4) a separate /home, this is the most interesting case, that actually will cause the installation to fail..
The problem is that in our live media (which are going to be copied/installed) /home is a symlink to /usr/home.
What happen when trying to install using a separate /home is that the destination filesystem will be mounted as:

rootfspartition mounted on /
home partition mounted on /home

later when 'tar' or 'rsync' try to copy /home (which is a symlink) over to the already existing '/destination/home' it will fail, because the mountpoint /destination/home is in use and isn't allowed to be replaced from a symlink.

The solution however is simple: when /home is requested, enforce it as /usr/home.
(that imply gbi/partition-editor should not suggest /home as a possible fs, instead /usr/home should be suggested).

to be continued ... I will do another round of tests using GPT layouts ...