Different submersible pumps will add different amounts of heat to the water, even external pumps can add heat to the water. I personally have never had any issues with my Mag Drives adding heat to the water, but some have had that happen. The Quiet One pumps usually run fairly cool, but I have no hand on experience with this.
The inlet to the SCWD is 3/4" hose barb, so ideally you would like the return pump to be of the same outlet size. I ran a Mag 12 through a SCWD on my 135 years ago.
The pump must be rated under 1400 gph also, so you will need to take that in to account when looking at pumps.
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