I realized that I can keep writing about bitachon post after post and not exhaust the topic while possibly boring everyone, so maybe I will have to intersperse other stuff. I left two questions hanging at the end of part 2 (part 1 here, part 2 here), but before getting to those, some other quick points.
1) I was beaten by a comment to posting the Yalkut Shimoni on the pasuk "Rabim machovim l'rasha v'ha'boteach b'Hashem chessed y'sovevenu (Teh 32)" The Yalkut darshens that the "boteach b'Hashem" might very well be the rasha of the opening of the pasuk! Of course, this fits perfectly with the opinion of the Ramban that even a rasha can have bitachon. By coincidence (I usually don't use the sefer) I saw the Mishnas R' Aharon vol 4 (R' Aharon Kotler zt"l) quotes this derasha and is perplexed at how a rasha can receive a positive response to bitachon. I am not sure if R' Aharon saw the Ramban (he refers only to the Chovos haLevavos), as it seems to me that the Ramban answers this question. Ramban notes that the pasuk, "B'tach b'Hashem" continues "v'aseh tov", to warn that although the rasha can call on the resource of bitachon and ellicit mometary mercy from Hashem, it does not mean that Hashem will wipe clean his slate of wrongdoing. There must be a follow-up of good deeds. See the Mishnas R' Aharon for his answer.
2) As mentioned in part 2, the Maharal refers to Hillel's bitachon that his home was not in danger when he heard a sudden outcry in the city. Maharal notes that the gemara is meduyak / particular in referring to a sudden outcry. Such an outcry could not be the result of the normal course of events, but must be an abberation, a departure from the norm, an almost supernatural occurance. That is why Hillel felt confident in calling on his bitachon. Where there is a clear intercession by G-d into mundane affairs, as evident by events being so out of the ordinary as to be unexpected and unanticipated, then a person has a right to assume that the events conform to Heavenly direction and the ba'al bitachon will be spared. I think the Maharal makes a significant point, but the question is where to draw the line. If someone walks off a four story building and thinks that because he is a ba'al bitachon he can fly, I think it is obvious that he is trying to go against what the normal course of nature is and will not succeed. But what about someone struck down by a sudden illness? Such an event may be sudden, but illness is part of the natural world. Some of the cases the Maharal himself uses to illustrate his point seem to fall into this area.