20gal mixed reef need help with coral placement

[Afaylenerich88]

Looking for opnions on what I should add next to my tank. Also any placement advice would be nice.

I'm going mixed reef. Looking for something to fill the top of the center pillar (high par 300-600+) high flow
Also the bottom portion front side of pillar low light area around (36-50 par) high flow.
Right side of tank- I'm looking for something in the range of (50-80 par) med flow above were the favia is placed.
Have an area on this side as well behind the setosa, about (80-150par) med-high flow.

Also I have some snake polyps. They only come out at night when my moonlight phase is on at about 6% blue spec, can't figure out if the daytime light is too intense or that's just how they are. Not a lot of info on these guys.
Some times during the day they are standing stright up. But polyps are closed. They have beautiful pink polyps when extended.
If you look closely you will see some baby gsp and some aptasia!! Oh no! Could this be the reason they aren't opening during the day? They seem to be growing and at night I try to feed the ones that are open. Also if you look there is a baby SP growing on the rock. Any advice would be great.

Thanks for taking time to view my thred. If you need more pics of areas I want to place more coral I will gladly post just identify what area you would like.
Basically any area that is empty that isn't next to the Nem. Can be filled just not sure with what.

PTR (providence tidal reef)
Sg 1.026,P04 0.025ppm,N03 0.10 ppm,Mag 1400,Alk 11,PH 8.2,Temp 78f
Cal 440