Disk management should first initialize (low-format) the HDD and then should be able to partition it from there.
Size of the partitions will depend on what use they'll have (large for games backup, like Steam games, etc., even larger for full HD movies if you have any), smaller than that for other media. Keep in mind that for effective disk management (occasional cleanup, defrag, etc) you need at least 15% of disk/partition free space, preferably more than that.
About defrag: you can set it up to run on a schedule for the HDD partitions, but don't do it for the SSD. It is not needed and actually will be harmful.
Heh, if you go that way, you could have separate partitions for each user and even more you could encrypt yours...LOL
How you divide them is up to your preference and ease of use.
One last note: IF the HDD happens to fail (hardware failure), all the partitions will be equally (in)accessible. Something to keep in mind; I have some HDDs that I use for periodic backups via an external dock, just in case. I fire that up once in a while to redo the backups, in case the main large HDD fails at least I don't lose all the data with it.
Of course, there are professional data recovery firms that can pull it from all but destroyed HDDs, but they cost a pretty penny. If I can avoid that, I will.
Any important data you consider irreplaceable should not reside solely on ONE HDD, regardless of partitions size, numbers, etc. That's why I keep these secondary backups. The HDDs used for backups should preferably be new(ish) and used sparingly.