With either the orange spot or the hectori gobi, would adding the tail spot into the mix cause some aggression? I assume the orange spot since it is also a blenny. I have the tail spot paid for already and found both of those other fish online available now. I would like whichever one will be eventually compatible with the tail spot, and do a decent job of algae eating.Orange spot blennies would work, hectori gobies are also effective hair algae eaters for smaller tanks.
As far as urchins, a tuxedo or halloween urchin could work. But I would recommend against a pencil urchin. I've seen them start eating corals if there wasn't enough algae.
Also, make sure it is actually hair algae and not bryopsis, as there aren't hardly effective bryopsis eaters.