I too don't believe that Mina was intended to represent Sooyoung, especially since early on the novel Rachel made a comment to Mina that she (Rachel) could eat what she wanted without watching her weight, unlike her (Mina). In particular, she mentions the weight going to her calves, if I remember correctly? Sooyoung has always notoriously been the skinniest member of SNSD who struggled to gain weight even if she tried, so it makes no sense that it's her.

But from the excerpts you picked out, that convinces me more that Mina is Tiffany rather than Taeyeon? I don't think Taeyeon has ever wanted to go to Hollywood but Tiffany, since going solo, has attempted to create a career in America, so I guess Hollywood falls more in line with Tiffany's desires? In relation to acting, I guess Tiffany has been in Musicals and intends to be in more, as she stated in an interview that she wishes to reprise her role as Roxy Hart(sp?).

Also! The weight comment makes more sense with Tiffany because back in like '09 I'm pretty sure Tiffany was one of the idols seen as having like "honey thighs" or something?

But I also thought at times that Mina or Lizzie was Yuri, and the reference to Lizzie's little sister might be about Yuri's cousin Vivian?

Ah! Sorry I've started to ramble!