Yeah, instead of over analyzing. just do a 1 week trial and error.
u weight ur self this week. then eat.
after 1 week ur weight is the same means you're not eating enough. then add more. (by more i mean as much as an extra full meal)
1 week later if still not going up, means add more again.
until u see ur weight go up, means u know thats about the right amount.
so all u need is an accurate weighing scale to use weekly

to minimise differences in water weight fluctuations and such, u need to set the best time to weight yourself.