Reply to Numark NS7 with V7

Im considering getting a NS7 to learn everything on, then in time i want to get a 3rd deck, the V7 being just a single deck from the NS7 would match perfectly, but would it work? NS7 usb to comp and V7 Usb to comp, 3 decks in total, output 1 of V7 to aux input of NS7, can serato itch support 3 decks? from 2 different pieces of hardware or would i just be better off getting a cd player going into the aux input? i know that i cant assign it to the crossfader, but i still have control over volume via the gain and eq treble and bass.