you should be able to make a diy
bulkhead from 3/4" pvc
parts ... I don't think you would be able to get a anything larger than that to fit.
you need a 3/4" slip to fpt fitting, a 1.25" o-ring, and a 3/4" mpt to slip fitting ... you put the female side in the tank with the o-ring under it, and then thread the male fitting into it from outside the tank.... hand tighten and you're all set - be sure to use generous amounts of teflon tape on the male fitting's threads
since your holes are 4" below the 'top' of the tank, you only need a small bit of pipe and an elbow, and the length of the pipe will adjust your water level. you probably want something like this:
which will prevent large debris from entering your drain.
for setting up a refuge and baffles, you can either glue glass into a glass sump with silicone, or weld plastic into a plastic sump with a solvent adhesive... or you can get a cheap-o rubbermaid bin, and for a refuge, just sit a 5 or 7.5 gallon aquarium inside ... the walls of the aquarium should protect the fuge from the turbulance of the sump
you could use a similar small plastic box to sit the intake of a skimmer in, so that it also receives calm water.