It sounds like you have listed all the possible minhagim. People do some or a lot of these.
I would suggest you ask your own personal Rav what is done in your community. A lot of people in my city do what is fashionable, not necessarily what their minhag is.
Personally, my minhag, (Yekkish) is not to wait until three at all. But we trimmed my son’s hair a bit before he turned three. On the day, we had a barber come in and give him a haircut, before a small buffet style party for family and close friends. We then went to the Rov’s house, and he cut a piece of hair from the tefillin area. The next day, he went to kindergarten (not wrapped up or anything), and the Rebbe who would teach him alef beis the next year, gathered the children round. They sang mazel tov, and he say him on his lap, put honey on a laminated card of the letters and read the first few with my son. And that was it. That’s all a lot more than I had at that age.
Just remember that for a typical three year old, it is quite traumatic to have all those big people around making a fuss, and you’re expected to perform, when all you’re interested in are the presents that you get.
Anyway, mazel tov and have lots of nachas