Hi pablo, regaring 1) TeX assumes that each character is a variable on math mode. You need to tell it that each "word" is, well, a "word":

\starttext
  \startitemize[packed]
  \item Valor actual neto: $\text{\em beneficios} - \text{\em costes}$. % you can use typographical variations inside \text: \em, \bf, etc
  \item Beneficio por euro: $\frac{\text{\em beneficios}}{\text{\em costes}}$.
  \item Beneficio obtenido el primer año.
  \stopitemize
\stoptext

2) will solve itself ather this. 3, I don't know.



--
----------------------------------------
Los fines no justifican los medios, porque la medida verdadera de nuestro carácter está dada por los medios que estamos dispuestos a utilizar, no por los fines que proclamamos.
----------------------------------------

“You develop an instant global consciousness, a people orientation, an intense dissatisfaction with the state of the world, and a compulsion to do something about it. From out there on the moon, international politics look so petty. You want to grab a politician by the scruff of the neck and drag him a quarter of a million miles out and say, ‘Look at that, you son of a bitch.’” — Apollo 14 astronaut Edgar Mitchell