I am sure quite a few people on here will raise an eyebrow or two … as not everyone will agree going from a perfectly good NS7 II with all the added functionality to a TT setup (especially with 20+ year old Technics) is an improvement LOL.
On-topic though. I guess you figured this all out and realise it’s going to be an expensive ride. Not just purchasing decKs (might want to consider the new Pioneers instead of getting the identical Technics second-hand) and a compatible mixer, more on that in a minute. But also the running cost, vinyl and needles to name the two most important ones. The monthly operating cost will be significant. Unless you are a millionaire of course, in which case you probably don’t give a d*mn about the cost 😀
There is two avenues to go to, either a compatible soundcard, in which case you can use just about every 2-/4- or more channel mixer really. The other way to go is getting a compatible mixer (meaning certified by the software you intend to use, Traktor or Serato. Mixvibes Cross let’s you use DVS/Timecode with any hardware). In which case it’s important to decide if you want the mixer to give you some midi control options as well.
Obviously all serious Pioneer mixers will work, as well as Rane (for Serato), Denon (X1600 for example), Xone and plenty of others.
It mainly depends on the functionality you want. If you want to do things batttle style, then a narrow 2-channel battle mixer might be the ticket. If you want things like FX and such, you’ll be better of with a more digital oriented setup.
Hope that helps