Denon all the way! Compared to the Numark, it excels in every area. It's overall higher quality, it's more compact and, while it may nor be easier to use, its whole feel will make you a lot more comfortable than if you'd choose the Numark. The Numark is built from cheaper components with cheaper labor and with less attention to detail, but retailed at a higher price than the Denon. I can't praise their units more.
A good mixer to go with this one would perhaps be an Ecler SMAC20, 30 or 40 (2, 3 and 4 channel, respectively),
a Vestax PCV275 or a Denon X-400.
The Ecler has slightly better sound quality than the others, while the Vestax is more rugged and is a tad easier to use. The Denon was specifically designed to be used with Denon CD players, so it has tons of features that you'll enjoy, as well as having the same width as
the DN2100F (so it looks neater). It has to be said, though, the the build quality can be a bit dubious if you're unlucky, but try it out and see what you think.
Another mixer that is really cool, and somewhat in your range is
the Vestax PMC25 or PCV25 (same mixer, but different faders), but it's only 2-channel so if you feel like expanding your setup with a pair of turntables later it could be a bit awkward. Pretty good sound quality, awesome EQ and 19" rackmountable, so it fits perfectly with that CD player as well, but not all people like it. Try it out as well, it might just be the one for you.