Regarding your first question I believe that it could depend on a number of this but if I should guess most likely not all disks has been included in the raid. Check with mdadm command wich disks have been included and verify that the raid is ok. I would recomend to set up the new raid array trough linuxmce webadmin, then you can monitor the progress and see if something goes wrong during the setup.
Regarding your second question: I managed to bring up an already created raid array when reinstalling lmce 810 from scratch. I first installed kubuntu 8.10 and then activated the raid with the command "sudo mdadm --assemble --scan", the raid device was then visible in the /dev directory. I then installed linuxmce and the raid array was automatically detected.
I do not know if this could be of any help, but I hope you manage to get your raid up and working again.