MorphOS and Open Firmware have LBA48 support, so there's no issue using large drives, but depending on which filesystem you plan to use there may be some partition size limits. SFS limits you to 128GB and for partitions larger than 64GB you need to use 1K blocksize. FFS I'm not aware of any such limit, but blocksize and buffers should probably be adjusted. PFS3 has a limit of 104GB per partition.