The things isn’t so much if you’ll learn quickly (btw I don’t think there is a way to speed up practice, it’s making hours and you can’t substitute time by something else like money), but that you don’t know what YOU want/need in a controller. Nobody, including us, can tell you what the best controller is for you at any given point in your DJ career. So what he might consider the most wonderful thing since sliced bread might be totally wrong for you.
The NV, while a nice controller, is a particular model and I have heard people that bought one and loved it and also those that regretted buying it. Either way, until you figure out what kind of DJ you are/want to be, what your workflow is/will be like and stuff like that, it’s really not a good plan to commit too much money towards your first controller.
I have no problem with used gear, especially starter controllers because they usually only get used in bedrooms and often get replaced after a year. So if you were to get an SB, MC2000/3000/4000, Mixtrack PRO 2/3, Beatmix 2 second hand you’d pay the smallest amount of money, can still recoup a bit of it when you sell it on when you are ready for your first upgrade.
I am a big Denon fan and can tell you that the MC4000 is great build quality and it has all the features you could need for quite a while. The only thing you might “miss” are the performance pads.