To your question about Ryn's penis size, this isn't a direct response like you were asking for, but Savin did post this on the Discord on the 12th of November, so it's very recent. Discord light mode content warning.
And I'm not writer, but it makes sense to me that it would be more work the more variables you added? So just because boob and butt size were deemed an acceptable amount of work by Savin - a person who chronically overestimates the amount of work he'll be happy to do - it doesn't necessarily follow that more tf variables would be okay. To which, again, not a direct source, but my two cents regardless.
So it seems pretty iron clad that there will be one penis size available to Etheryn once uncaged, and it will be 7 inches. As to whether that's a reasonable size in lore for a half-sexed elf, we do have parser text which suggests Synneva has somewhere between a 6-6.99 inch penis.
So, Etheryn having a 7 inch penis would be a bit larger than Synneva, but also seems within the realm of natural variance.