Boy, that’s a bigger question than you may realize.
Music production in Ableton is such a broad thing, so the first question I’m going to ask, which will inform pretty much the entire conversation – do you know how to play piano/keyboards?
You aren’t going to be able to replace your Mixtrack Pro with it in Serato – Serato needs a proper bit of licensed hardware at the core of your setup to run, the MTP is, the APC40 isn’t. The other thing is, DJing with an APC (and Ableton) is not meant to be the same experience at all as DJing with the traditional 2-decks-and-a-mixer format, like Serato and that gang. It’s honestly something that I don’t have enough experience with to be able to give you a whole lot of input on.
As a producer who doesn’t DJ in Ableton, I’d say you might be better served by getting something that has actual keys on it. I have an Akai APCKey 25, which has a lot of the features of the APC40, but also has keys that you can use for entering your notes.
This post has been a little disjointed, sorry… at the end of the day, I think the takeaway from this is going to be – make sure you know what you want, why you want it, and how you’re going to use it, before you throw too much money at it.
Production is a very big box to open, a whole lot of fun, but the workflow is something that will take you years to perfect. Do full research, asking questions on a forum is a start, but you’re going to need to really dig into this – not because of the expense, but because you have already committed yourself to a large learning curve.