Hello HenW, all,
I can also recommend creating a new HDD from scratch. In one of the threads of above mentioned forum there is a link to download the SW for creating an USB stick. It is then to be attached to the BM 5. While startup it must be sure to boot from the stick. there you not only can clone the HDDs but also create a new one. I did this and have seen a little bit „rough“ BS5 system, but after fetching the updates all was fine. Best way is to perform this with an extra HDD and keep the original as a safe backup…
To your questions, the MB should be small and be the boot partition. It has to be set to bootable partition.
I also tried the recovery, once, working also fine. It may also be needed to perform a SW update. While recovery, the system partition is refreshed from that. I believe, data is not touched.