From what I understand, you need RB4 in order to use the NXS2 decks–RB4 enables you to use multiple Hot Cues, colored wave forms, etc. In addition, RB4 is really no different from RB3, it's actually much better.
Whomever told you there's limited USB correction is incorrect. I use a 256 GB SDD and have a 64GB USB flash drive with no problems.
Hope this helps.