You might also consider adding an acrylic overflow box. Without it, you’ll want to make sure the in-tank pipes and fittings are 100% watertight (ie solvent welded or threaded with thread tape; not just pressure fit). Otherwise, when your return pump is off, you’ll be at significant risk of all of your water draining to the sump and, assuming your sump is not massive, onto your floor. For example, if you have a slow leak at the bottom of one of the pipes inside the tank, given enough time without the return pump running, the tank water level will drop to the level of that leak. All water above that point will end up in the sump.
If you install an overflow box - and assuming it’s leakproof - you’ll limit the amount of water that could drain to the sump to only what’s in the overflow box.
You’ll also want to make sure that, in normal operation, the drain is plumbed to take water close to the surface. If you use the one pictured above, when you turn off your pump, the tank will drain to the top of the strainer basket. You can probably rig an internal surface skimmer (like the inside part of a ghost or synergy overflow) or DIY something to act as a surface skimmer. That’ll keep more of the tank water in the tank when the return pump is off.
Personally if it was mine, I would either plumb a closed loop in the holes for circulation or just plug them with bulkheads and plugs. I’d drill the back for a low profile overflow box like synergy, Fijicube, etc.
