Avi K, the Rambam says “all” to exclude all of the exceptions that he just listed (in that very Halacha) that apply to a milchemes reshus.
As for the talmid chacham in Shulchan Aruch, that refers to someone who is on the level of Torato omanuto. No Internet, no newspapers, no radio, no chazzanut concerts, no talking about politics or the weather. Only learning (although some say that he can work in order to earn a subsistence income).
True. But the Shulchan Oruch Y”D 246:18 paskens that learning Torah takes precedence over any mitzva that can be done by somebody else, and does not specify that this only applies to a Talmid Chacham.