I personally would not form out a bunch of money. I was in a similar situation in that I have a Numark 4trak at home and play on cdj2000s. I would suggest having a look at Mixvibes Cross software and use your S4 with that. You can set your cue points in it and sync it with rekordbox. It also has harmonic notation 5A 4B that you can write in the comments section to appear in rekordbox.

Personally, having gone from a 4trak to CDJs in a club off a USB, I did not find it a huge leap to be honest with you. I found preparation in rekordbox to be the key. I made the switch to Cross because it had the harmonic key notation and the cue points comments and playlists are synced to rekordbox.

It also has HID integration with pioneer decks so you could use your laptop in future if that is what you really want.

Watch the cdj2000 overview clips on YouTube a couple of times and you will be fine.