Plumbing, A few new Questions

[spoot]

If you want your skimmer pump to be fed from the overflow pipe, your overflow GPH, and thus your return pump GPH must be higher than the mak 4 GPH (which is ~1100GPH). The excess water from the overflow would be tee-d off into the first chamber of your sump.

If you just want to have the skimmer fed from the sump, all you need to do is drill 2 holes in the sump. one for the skimmer pump and the other for the skimmmer drain.

Are you going to have a refugium?

Make a sketch of your plan in ms paint and we can work from there.