It is very exciting when you see all your hard work begin to take shape. It is begining to look like a reef, nice job!
I would be careful with what you add. You really should not add anything you cannot test for. Iodine is very difficult to test for. I do add magnesium (my tanks run low) but I test before adding. Actually, if you keep up with regualr water changes and use a good quality salt mix, one for reefs, you shouldn't have to be too concerned. Are you planning to use a PH buffer? I have found that is absolutely essential otherwise my PH is low. I like the 2 part PH/calcium, very easy to use. I have my tanks figured out but in the begining I tested daily (first couple weeks) before adding. Now I will spot check to catch any flucuations. Try not to get ahead of yourself, it takes time and utiil I see ammonia 0, nitrite 0 and nitrates begin to climb, I let it do it's thing and add nothing.
With damsels, I found out size dosen't matter, (mine were small) they were attacking my octopus like a pack of wolves. After seeing them repeatedly bite his arms every time he tried to emerge form his den, I would not trust them.