3 requires events or at least use of the death-related event ID... I don't hack FE8 so I'm not sure but try looking at the death quotes for main characters and seeing if you can figure out something from the patterns
for 4, look up a music insertion tutorial online, there should be a few. it's not easy though and generally takes some work to make it sound good (since it's MIDI music with hardware limitations and all), plus they're generally geared towards FE7 again, which is part of why people generally don't hack FE8 (it's kind of a self-fulfilling cycle or whatever of "FE8 is too hard to hack since you have to figure things out on your own, so hack FE7, which only increases the amount of knowledge of FE7 hacking there is", or something, lol)