4.8 release? there really isn't any reason to be building ports at all.. the requirements will well exceed the partition size.
That is a very strange layout, I'm not sure why you chose those sizes.
Use packages to fit within the alloted space, while I can't be entirely sure from that partial layout.. but a partition immediately proceeds /usr which would prevent growing it, perhaps you could recreate /usr if you reserved some space near the end of the partition.
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