Ma’aser and/or Mitzvah

Shalom aleichem Rabbi Lauffer. From Mishnah Berurah 656:8, it is clear that the same procedure used for ma’aser kesafim is used for spending money on mitzvos in general. Quoting the MB there: “See the Magen Avraham and Elyah Rabbah that just like for the purpose of charity the tithe is taken from the principal in the first year, when it has been earned, and from then on from the profit which derives from it, this is also so with respect to what is discussed here.” Given that the same rule of a 20% limit applies to both ma’aser kesafim and mitzvah expenses in general, if a person does the mitzvah of ma’aser kesafim min hamuvchar, which is 20%, would he be exempt from expending money to do any other mitzvah? Or when they say that one doesn’t have to spend more than 20% of his income on mitzvos, is it only talking about the income that remains after giving 20% for ma’aser kesafim?

Thanks a lot.