It's probably hard to generalise, since there are any number of other traits that make someone a good lawyer, apart from those shared with doing philosophy. However, I understand that law firms are very interested in taking people who have done a philosophy degree, and a good number of philosophy students show an interest in studying law. Several skills that are very important to philosophy are also important to law, in particular the abilities to make sense of abstract information and convoluted sentences, to construct arguments on both sides of a case, to anticipate objections and prepare replies, to spot fallacies and weaknesses in arguments, to integrate a wide range of different kinds of relevant information, and to write and speak clearly and persuasively, breaking down complexity into simple components. There may be other relevant traits that help as well, such as an interest in what is right or just, a good memory, motivation for hard work, and so on. On the other hand, IF philosophers are characterised by an interest in the truth, and IF a good lawyer is one who is interested in protecting their client or success (assuming a combative legal system like we have in the USA or UK), then there can be a conflict of motivation in the two professions, which would make philosophers bad lawyers unless they become public prosecutors! But these are big and controversial assumptions.
I can answer the second part of this question, but not the first (sorry!). The claim that 'everything happens for a reason' is known as the Principle of Sufficient Reason. It is commonly associated with Leibniz (and before him, Spinoza), but played an important role in German idealism, and was the topic of Schopenhauer's doctoral dissertation. You can find the references for these and other discussions in this article from the Stanford Encyclopedia: