I have to add. like Howard, that my Toadstool Leather also deflates, goes green, retracts it's polyps and goues slimy. I panicked thinking it was dead however a week later it perked up and seemed to have grown bigger & brighter. In my experience, my Toadstool does this once every few months.
This may not be the same case but just thought I'd let you know that this happens...
I absolutely love my Betta 1300. I've had Orcas and a bespoke tank before and this tank is my favorite so far. The sump is a good size, the four sections are adequate - althought a fifth would be great! The tank has bevelled corners. Comes with pretty much all you need except lighting which is better as your not stuck with someone's elses idea of "suitable lighting".
Downsides are; high evaporation so I have always fought higher than normal salinity and a black weir (stands out on a blue background).
No problem. Never thought I'd be giving you advice!
Zoas should be fine there. People tend to have them mid level to bottom to avoid strong currents but they also do well under light. Personally I would leave them there and see how they get on. No need to feed them. They will pick up bits of food which passes by (particularly the Parazoanthus). They'll be fine while your tank cycles.
Oh dear, it sounds like an Asterina Star. If it's legs are "stumps" and varying lengths it is. If you're not keen on getting rid - as it might be an algae eater, you're best to keep an eye on it. If it tends to stay away from your coral its an algae eater. Personally, again, I never risk it. Note they drop a leg in order to multiply.
The sessile thingy sounds like Tube Worms / Fan Worms.
Not sure about the last one, sorry. All I can think of is a Spoon Worm but that's a wild guess.
Looks great! I always try to create caves like yours as well. Unfortunately it's doesn't always work or look right once you think it's all done! Can't tell by the pic but you might want to make sure your powerhead isn't pointing directly at your Zoas otherwise they may not open up.