In the middle of buying lot in Black Sand Sub

[kalakoa]

is it safe (relatively) to potentially purchase land in the black sand subdivision

Wrong question. Land is always a good investment, even when it's over a much longer timeline than intended.

Are people even allowed to go down that way, or into the subdivision?

Better question: will access and/or development rights suddenly be lost at County's whim?

There are other subdivisions with "lax building codes". Personally, I can't imagine living on a tiny lot ever again.