I'll try to remember them as best I can
1) Chen's event on 4F (5F and 6F are the follow-ups) is about Chen trying to find Ran, I haven't translated it, so I can't say anymore than that. And with what Hawk said, you need Chen's BP to trigger it.
2) The Marisa/Reimu Event is either the one where you need a certain amount of BP with Wriggle to trigger OR it's about Marisa finding what I called Mysterious Scrap of Iron (there was 2 other of those in the previous floor, which makes a grand total of 3, and they are currently consumed for me, but I don't know what it made)
3) There are quite a few of those, and I assume you're talking about events that are not when you go into one of the option in Gensokyo (i.e. Hakurei Shrine, Magic Library, etc.). I'll list those I can think of.
- The first one you'll ever get is when you first come back, they talk about god knows what and the game then tells you how diving out of the dungeon works (you get back all HP, MP, TP back, bla bla bla).
- The second one will be when you first recruit a character, whoever it is, and they talk about stuff again, and the game tells you how to change characters at the Human Village.
- The last one I can think of is one I got when I first loaded my save in the new demo (after beating Komachi basically), but I haven't bothered looking at that one, so I don't know what it's about.