what are the differences between damage types + how to ignore iframes using the "deal damage" block

1. Do damage types matter other than the death message?
2. Is there a way to deal damage ignoring i-frames (when they turn red) but still have effects? (like knockback)

Questions regarding custom damage types:

1. Is there a way to make it display missing hearts? (like how when a player attacks)
2. can you make it ignore iframes?