The pump output will need to be split to accommodate the dual returns. The returns should be the same length or the longer one will not flow correctly.
If there is space in the stand behind and above the sump I would angle the return to the middle of the stand and split the return there securing the plumbing against the stand. Use a section of flexible tubing between the sump and the pump and between the pump and the returns to absorb vibration noise from the pump. The longer the flex the less vibration will be communicated through the plumbing.
You will want to use a bulkhead fitting on your sump. Make sure the ones provided work. Some of the ones that come with the tank are cheap. Aquarium Village sells them if you need.
You will need to match the plumbing from the display tank bulkhead fittings with the output of the split and match the input of the split with the output of the pump, probably 1." For space issues you may have to use a Tee but a Wye is more efficient in terms of flow.
http://www.hottubspasupplies.com/Hot-Tub-Parts/Fittings-Plumbing-PVC/Wyes
Also, instead of one 90deg fitting you can use two 45deg fittings more efficiently. I shorten the 45deg fittings by shortening the ends of two of them and connecting them.
If you want to use your main pump for your reactors then you will need to TEE off the return pump for that also. With this you will want to use a TEE with the straight line of the TEE going to your tank and the 90deg ported to your reactors. After the TEE you may need a valve to restrict flow to your DT enough to power your reactors. You will also need a valve before your reactors so you can isolate them for servicing.
Make sure all this plumbing is secure.
Plan out which side the return pump will be on to minimize the amount of plumbing and minimize the amount of space taken up. Looking at that pump I could see it working well with the return on the right side of the stand.
Your drain going to the sump should be pretty easy. The tank bulkheads fit into PVC which flows into the filter sock area. I would use a WYE here also so the water does not crash into itself.