Reply to Newbie with full TT setup, looking to add toys

Hey guys, I've been doing mashup production for about 6 months now and I'm trying to get into the performance/DJ side.

My current available configuration is: 2 Numark TT200's, a Numark X6 mixer, and an Audio 8 sound card. Using Traktor, I could use that setup to mix my tracks with Deck A and Deck B and run some effects of off my mixer to play with those tracks.

Now, what I would like to do is add a trigger pad to throw in a) random sounds or b) use loops on Decks A & B and play with cues on Deck C & D. I'm looking at buying an MPD18 to do this. A few questions, though:

1. With the 16 trigger pads, would I be able to designate 8 to Deck C and 8 to Deck D? How would I be able to make that divide?

2. How would I assign the pad in general to work in Traktor without going through the mixer, since there are no RCA inputs? Does Traktor auto-detect devices like that?

And now to go a bit deeper into the grand scheme...

3. If I'm not scratching, do I really need my damn turntables?!? Couldn't I really sell them off, buy a controller and be good to go?

Orrrr

4. Could I keep the TT's in order to be "legit" and replace the mixer with a full controller? Would a controller allow me to queue up songs on all 4 decks?

Sorry for the load of questions right off the bat, but this place seems to hold a wealth of knowledge. Thanks in advance!