Slip-on's do not make as big a change as a complete exhaust. K&N filters that are designed to replace stock filters also are not a big change. Of course you now have two changes, but, my opinion would be. The stock controller has some ability to adjust. You would still be OK. If you change to Big Air Kit, pods, or etc then you might think of a fuel controller.
Just an amateur opinion so take it for what it is worth.
You made a good choice in bikes. Looks good, runs good, sounds good, so maybe that's all you need. You can spend a couple thousand and gain 10 or 15% power, all in what you want.