This question is asked by all of us; "How much experience is enough..."
There are lots of shared experiences above, but the only correct answer lies in you. You will undoubtedly get a lot of responses with extreme claims from they knew nothing, bought a boat and sailed it expertly after leaving the dock to those that claim you need many years and formal safety courses and every bit of safety gear. There is tonnes of grey space in between.
The fact that you are asking the question with the feeling of worry about being in over your head might indicate that you aren't ready; Although, that depends on how far over your head you feel it is.
Perhaps answering some questions might help; Do you know what type of sailing you prefer? A laser is far different than a 40' keel boat, each are pleasurable, but which is right for you? If you have enough experience to decide what type of sailing you like, then you'll probably start to get a feel for what type of boat you'd like. Do you want a new, racy Melges that requires a crew to sail or do you like classic boats with a heavier displacement for longer solo missions? The process of answering the above questions gives you practical experience that will sneak up on you.
Experience will also save you money. When you sail on other people's boats, you will find what equipment and rigging you prefer; simple things like using self-tailing winches and standard winches will let you know if that is something you want to have on your boat buying checklist. Experience gained by spending time with sailors will let you over-hear conversations on re-coring a rotten deck or the different benefits of gasoline vs. diesel. This type of valuable experience saves you money from making poor choices (for you) when buying a boat.
If you have little or no experience, how will you know if you even ENJOY sailing? Why invest the money if you can't answer that question.
There's the answer to your first question.
The second question I can answer specifically. I spent probably 6 years or so sailing on other people's boats and trying everything from wind surfing, lasers, J22's, J24's, Shark 24's, Mumm/Farr 30's, an IMX38, Beneteau 36 and a handful of other cruiser-types. I tried club racing, "off-shore" racing (great lakes, isn't exactly off-shore, but they still call it that), messing about in the Caribbean and even sailing a paraw in the Philippines before deciding what my dream boat list looked like. Of those 6-ish years, at least 3 were searching for the exact boat for me.