Sounds like a fun project! A few comments:

Water flow through the sump may be a little too high for the fuge "section", you may want to consider another small tank (10g) for a fuge with a powerhead supplying water flow from the sump? But this will greatly complicate your plumbing. Or you could bypass the fuge section with most of the sump waterflow somehow??

I have been told that the CPR overflows are junk! I would get one from Dan, or beter yet have your tank drilled for an in-tank overflow.

Best submersible pump IMO is an Eheim

Have fun!!