Well, there's technically a difference between what is called the "Basic Rules" and the "SRD." D&D Beyond, so far, seems to use the term Basic Rules to refer to the SRD, which I'm pretty sure is erroneous. The Player Basic Rules include I think 6 Backgrounds, whereas the SRD only includes 1. I assume the player options available in the beta will include both what's in the SRD and what's in the actual Basic Rules, since they're both published by WotC for free online. It's obviously the DM's call, and I will put a question in the Beta forums to find out what will be in the character creator beta, but for the purposes of this RP (to test out the digital tools), I think using the expanded list from the actual Basic Rules would work.