NPCs are allowed in public player housing as long as they provide a service. That said, sadly a beholder isn't quite appropriate.
Anyway, prices for player housing depend on the region. Given Luskan isn't so posh, it's cheaper. But it might also depend on the tileset you use... For the temple look I'd say 10,000 per tile. Like I said, there's a forum somewhere if you want to dig it up.
And yeah, there's a reason they call them picket fences. Ironic, that they are now staples of the typical innocent suburbia. That said, picketing does leave telltale marks and damage (bruising, scoliosis, etc.); just not super obvious stuff. Do be careful how detailed you get with that stuff though, we do like to keep the server PG.
Also, keep those feet dirty. Evidence suggests that's how wine was serendipitously made in the first place - from the yeast between someone's toes! Talk about a dose of toe jam...