I believe you are right, in the case of Alani PS4 users get her upon her release without having to complete the associated challenges. However, I do think that she will be released on May 3rd, but I’m not 100% on that. If so, PS4 players get to play as her straight away while the rest have to complete her unlock challenges. Command rank 42 is a good guess, though I think it more likely that she’ll be available at level 4 and the other four characters will only have challenges and not unlock levels.
I would assume dlc characters will be available from download right away with out level requirement
with that said xbox players will wait.