Regarding the first question, the first example emphasizes the ambiguity of the amount, as well as the separateness of the two different groups. The second example implies an indeterminate amount without emphasizing the groupings. The word "some" would be contrasted with "a few" or "a lot". Incidentally, one could also phrase the second example as "I saw some people and cars."
The word "some" (and "a lot" or "a few", "many", etc.) are quantifiers. It may be used with both countable nouns (nouns that may be individual counted, such as cars, people, trees, etc.) and non-countable nouns (such as experience, wisdom, light). The phrase, "I have some experience and some wisdom," would emphasize the vagueness of two different non-countable nouns, and presumably differentiate between them (experience and wisdom being separate). In the example "some people and some cars" would also presumably emphasize that one was not emphasizing people in the cars. "Some people and cars" would emphasize the fact that not a lot but more than a few people and cars (and people in cars) were seen.
Regarding the second question, "in good hands" indicates an individual is safe or cared for. As a commercial example, consider is the Allstate logo of the hands indicating care.
The "with him" indicates an individual, and the slightly awkward appending of "here" indicates the "him" is present in the immediate locale.
Consider the phrase, "With John here you are safe"; substitute "John" with "him" and "you are safe" with "you're in good hands", and the sentence is equivalent. "With him here you're in good hands."