Unless you planned on a sump full of overflowing dividers and sponge traps, why not just put it into service right away.
A sterlite drawer unit, full of media for a filter/bio tower would get you going in no time.
See how it performs for you.
A sump in use, is way more beneficial than one in planning.
If the food goes by so fast you only get to take a bunch of small bites or slow enough to relax while you eat.
End result is the same.
The small bites might take a bit longer to finish the meal, than slow, steady feeding.
Fuge, scrubber, or both.
They both require about the same hardware. A lighting source.
A bit of extra plumbing for the scrubber, depending on style, or layout of your sump.
Every tank being different, would be hard to suggest one over the other.
Toss some plants in and check your water after a couple weeks.
That should tell you what you want to know.
$0.02
Just my opinion, and we all know what opinions are like.