The one that is always needed is your root partition. The preferred one to not leave out is the swap. That makes swap paging much much much much more snappy. EXT/Reiser does not handle files well (kinda like how windows would operate for example). Linux is that way at least. BSD may need it, I have never tried UFS without swap.
When creating the partitioning setup do the following:
Partition 1 - NTFS
Partition 2 - BSD slice
That whole thing will now encompass all you want on BSD. Within that slice, you can create partitions like the root and swap.
As for sizes, 10 each should be fine. Make the swap an even 512mb for simplicity or if you feel like probably overdoing it a wee bit, go for 768MB.