Make a new event in the LuaText module section for PLAYER_REGEN_ENABLED and PLAYER_REGEN_DISABLED. These are your combat flag events. Ripping apart my threat tag would reveal this.
if UnitAffectingCombat("player")==1 then
return "%s %s",UnitHealth("player"),UnitHealth("target") --see note
May also be Health(), I'm a bit foggy on the LuaText shortcuts the team did. For boss health, you would check UnitClassification for boss, then make separate tags for them. For the level 80 one, there is probably already a coloration option for that somewhere, but worse case just compare their level against yours, use |cff%02x%02x%02x%s|r in the return, and make a formula based on what colors you want. Lets say you want it to go from yellow to green, you would use %02xFF00 and the variable for the level discrepancy would be used to scale the first color (red). It's a bit tricky and I have some code I used with hit points to help you out with this. For the last request, see the first.