An easy way to ask about parking is something like “where do most employees park and how much does that come to each month?” Most people will tell you in their answer if the company makes any parking arrangements. My company doesn’t reimburse parking. However, employees that work downtown (where parking isn’t free like it is in our satellite offices) get an amount added to their paycheck each month as a “transportation allowance.” You can use that on parking or on public transportation depending on your preference. (If you carpool or live within walking distance–you can just pocket it!)
Most of our candidates ask about benefits when they get an offer. There’s a pamphlet HR gives them along with the offer that details all of our benefits. Those pamphlets usually include vacation and sick day policies. If they don’t, I don’t see any problem in asking about it. I wouldn’t get into how your last employer handled it (it could sound like sour grapes). But there’s nothing wrong with a straight up “what are your vacation and sick day policies” question.
I would ask HR about parking/benefits/vacation policies. The hiring manager may not know what is standard for new hires. (I have to remind my own manager each year how many vacation days I’ve accumulated–she can only remember her own).
Flex time is a bit trickier. We do have a corporate policy on flextime but whether you can take advantage of it depends on the manager. Some have no trouble with flex time. Others don’t allow it. If it is a dealbreakyer, you should ask after you get an offer. The suggestions given here about how to ask are good ones.