Is your old device broken beyond starting?

To 2) Before installing CSSU-thumb decide, which kernel you want to use. Either kernel-cssu or kernel-power.
To 3) There are informations about the installed packages and their status in /var/lib/dpkg/info and in /var /lib/dpkg/status, but those files are not easily readable, because of all the dpkg info/garbage, that is part of the package management

Personal note:
My approach with an older, but still working N900 was the following:
1. Install rootsh, backupmenu and kernel-power stuff into the new N900 and reboot once to the fresh kernel.
2. Verify the kernel version to be the same on both devices.
3. Create a backup of the settings, favorites, package list and contacts/communication with the built-in
Backup application on an external microSD card of the old device.
4. Create a rootfs-only backup with BackupMenu again on the external microSD card.
5. Transfer the microSD card to the new device and boot into backupmenu.
6. Restore the rootfs-only backup from the microSD card to the new device.
7. Reboot into backupmenu on both your N900.
8. Connect both devices to an PC running Linux, either installed or Live-CD will work.
9. Transfer the complete content of the internal card of the old device, /dev/sdX, to the new device, /dev/sdYIf you are unsure about the device names, attach only one device at a time and 'dd' the content to the PC first, later from the PC to the nwe N900.