You can use Advanced HID with Serato just like you can with Traktor. HID was actually added to Serato way before Traktor, and Serato supports the CDJ 850s which Traktor does not.
If you’ve never used CDJs then sticking to your S4 for the set is your only option really. Try and get more private time on them if you want to be able to use them well for gigs. If you have your S4 set up you could set the CDJs to control decks C + D for full 4 deck control during your practice hour.