The Rambam did not Shnor from his brother. He invested with his brother and his brother did not charge him a commission. When his brother was shipwrecked, he lost that source of income and ‘mamon rav’ of his investment (Igros Harambam, p. 229). I think you will also find that he STUDIED medicine even before his brother was shipwrecked.
The Rambam also holds that there is a Chiyuv to know the entire Torah (Hilchos Talmud Torah). Reb Moshe (Igros Moshe 8:36:4) writes clearly that according to the Rambam a person can and possibly should take gifts or even Tzedakah until he gets to the point of full Yedias Hatorah. Now, THAT would make me think twice before using the Rambam to assuage my guilty conscience.