Regarding the incest, while it’s true that there was some dynastic incest in the middle ages, GRRM likes to go far beyond that for some reason. Remember, there’s not just the Targaryens, but Jaime and Cersei too. And let’s not forget that creepy wildling dude (Craster), who slept with his daughters, or that scene were Theon fingers his sister Asha. There are many other, smaller mentions of incest sprinkled all throughout the series, like the Fowler twins, who sometimes do threesomes with Arianne, or Euron, who is implied to have raped his brother. Furthermore, George originally planned for Jon and Arya to fall in love too – and that was before they would find out about Jon’s real parentage, meaning they wanted to bang while they still thought they were brother and sister. Thankfully George abandoned that idea when he wrote the later books, but the fact that he even considered it tells you a lot.
The point is, ASoIaF has way too much incest to just be ‘historically accurate’. It’s more likely to me that the idea actually turns George on.