wisdom needed...new 75

[newtofish2]

I have recently aqcuired a 75 gallon bowfront with 15 gallon sump, CPR siphon overflow, return pump, deltec skimmer (for sump or hang on back), another smaller hang on back skimmer, lights and all the plumbing. I am moving my overstocked hair algae infested inhabitants into thier new home...eventually. I currently have a 30 gallon and 20 gallon that will meld into the 75 (30 has a hair algae problem...overstocked and my 2 year old 'fed' the fish a whole container of food on boxing day.)

I have 2 clowns, 1 orange spot goby, canary wrasse, and 2 damsels, 40 lb live rock and various corals.

I have cleaned everything, and patiently filled it with clean RO water and I cant seem to keep a siphon with the CPR ...the aqualifter doesnt seem to be working?

Also I am reading about the hazards of flooding (and drowning of my toddlers in the sump) with the CPR overflow I am losing confidence in the sump set up with the CPR...

Could I just run the deltec skimmer 600 as a hang on the back (it does have a place for carbon or media ) and add more live rock ...would that be enough?

Should I add a canister filter? or something else? or keep trying with the CPR...a new aqualifter...and better child locks on the cabinet?

Thank you for your help!