A lot of my essays (math or otherwise) are assuming a certain level of internal consistency with the worldbuilding, but as much as GRRM does make mistakes, it hangs together better than people often give him credit for.
As for the population-to-troop ratios, since that stuff started with Elio who’s in a better position than anyone else to check with GRRM about whether his estimates were right, I feel more confident about that.
Re: Robert’s spending, I would be more worried about that stuff if GRRM hadn’t written the Tyrion chapters which strongly hint that LF committed fraud.