Roose's motivation with Ramsay was to use his body after a death embrace -- as Ramsay has those genetic traits he needs -- Ramsay was purposely raised as a bastard that hates everyone so that he could become the greatest evil personality - even better than Roose him self -- when they hugged in the show Roose took his body then stabbed his own old body --
Littlefinger has all the money in Westeros from his time on the small council as the Treasurer - aka Master of Coin -- he can pay for all deaths in Westeros he needs to move about -- and he can hire sellswords as he needs -- people change and evolve through death -- and I suspect that in the latest life of Brienne, who herslef died in the bear pit, she became a sellsword of sorts -- the book lays out characters better, the show is way past haywire as Brienne's arc is not to have a baby with Tormund who becomes Mance Tarth I'd suppose and the new generation at the end of the story that saves the planet as a warrior Free Folk -- in the books that character is the baby Gilly is protecting -- Aemon Steelsong
Roose didn't need to teach a son to read who wasn't needed for anything other than his evil body and mind -- when most people die they become less of them selves -- but in the evil Red forces they become more of themselves -- Roose became more evil and gained more power throught his effective murder of him self .. LOL .. if you are willing to believe that -- and I am completely serious ..
post Roose death/Fat Walda death+baby death Roose gained extreme power - in a way to appease the Red God R'hhlr and move on towards greater evil powers in the totality of evil
The show hints that LF wrote it -- I suspect he did in the show -- maybe Roose did -- a literal man who was taught to read and write as a noble -- wrote it .. we shall see in the end as not enought is factually known now -- heck, it might be better left alone just so that people can speculate such as you and I are now -- not everything needs a definitive answer - unanswered questions generate fantastical thoughts -- part of GRRM's motivations