Oh, almost forgot: I don't think I can split the cost of the flight with
the safety pilot, can I? Since I wanted to go practice instrument
approaches and asked/needed someone to be my safety pilot, the SP is no
longer "just a passenger". Since his presence in the airplane is not
coincidental, I'm assuming that I can't charge him 50% of the cost.

In the literal sense of the word, you can't "charge" him anything
without holding a commercial ticket. You have by the way, ruffled my
feathers here. First, I, personally, wouldn't ask a stranger to ride safety
for me. Second, asking someone I know and trust to ride safety for me is
asking them for a favor and I wouldn't have the temerity to require them to
compensate me for doing that favor. I dunno, sounds kind of rude... "Hey
Billy Bob, will you pay me $50 an hour to be my safety pilot?"