I would personally go with the NI cards, purely because they’re cheaper than Serato’s RANE cards and they achieve the exact same thing, and with proper care they should both last you a life time.
Again, personally I would go with Traktor, purely because it is a far more capable program. Serato scratch is very bread and butter in it’s approach, whereas Traktor gives you a ton of options which, if you ever decide to integrate a controller into your setup for some effects/remix set fun, which you probably will after you get used to Traktor, then it costs you nothing to do so and you’re already familiar with the program.
I just got a new laptop because my old Toshiba Satellite, which ran windows 7, struggled with the recent version of Traktor Pro 2. It’s not so much the brand of laptop that matter, but your processor and RAM. Ideally, you want as much RAM as you can get, but processor wise you want to be aiming for one of the sandy/ivy bridges to guarantee that Traktor Pro 3 will not eat your CPU (whenever it is that comes out). Download the demo of Traktor, put a song in all 4 decks, put them all on at once, and start putting effects on them all, especially effects like Delay. If it starts popping/clicking, you need to optimise/upgrade. Or just not push Traktor that hard.
You don’t need AV splitters. You need two more AV cables, and the time code vinyls. You run the turntables output into the sound card, this in turn puts it into Traktor which applies it to the track you have loaded into the deck, this then is sent to the output of the sound card into your two separate mixer channels, voila! Just like having every record ever on vinyl. Dream come true, right?
Obviously I’m Traktor/NI biased, but I do believe on a level playing field, Traktor is the greater program. Some people report stability issues but I’ve never had such an issue with it, though I’ve also never seen Serato fail either.
If you have some spare cash lying around, I’ve heard nothing but great thing about these when using Traktor:
Always good if you feel like getting a bit of controllerism into your set up!
For comparison of processor power, my laptop is an i5-3210M running Win 8 with 8 GB of ram, and the CPU load bar doesn’t even budge when I’m pushing every function of Traktor with <5ms latency on my soundcard (as in, unnoticeable by human ear). My desktop is an Intel G870 3.1 GhZ dual core with 6 GB of RAM, and I run this also on the same settings albeit with 6.5ms of latency (which is unnoticeable also, but 5ms is the general consensus around these parts). My old laptop had an AMD Turion 64 X2 2.2 GhZ, with 8 GB of RAM, and that struggled with Traktor. Although it was 5 year old so, I guess that might have something to do with it, but yeah, not latency underneath 20 ms and even then it still popped and crackled.
I hope that’s answered every possible question you could have on the matter, and give you a clear idea of what it is you need to buy for your DVS set up
(You’ve got most of the expensive stuff already, with the looks of it!)