Also kind of depends on what you mean by offender... Some Empath Offenders still take Heal Other/Absorb Pain/Resurrect, while others find most of those unnecessary.
These were the original Green Machine (all empathy offender) build requirements, I should note they don't mention IOs because this SG is from well before the Invention System existed and were just never really updated since then.
Heal Aura - required, 3 heal recommended, no recharge or endredux needed
Heal Other - not required
Clear Mind - required by level 20
Fortitude - required pick at level 12, slot with 2 defense at a minimum
Recovery Aura - required pick at level 18, slot with three recharge as soon as possible
Regeneration Aura- required pick at level 26, slot with three recharge as soon as possible, slot 3 heals in as well.
Adrenalin Boost - required pick at level 32, slot with three recharge as soon as possible, strongly recommended to slot 2 heal, 1 endmod as well.
Blast Powers
Slotted Attacks are required, this is a project that is expected to kill things.
Your blast nuke is a required pick at level 38. Don't worry, no end drop will bother you.
Pool Powers
Hasten - required by level 18, 3 slotted
Assault - required by level 24
Tactics - required by level 24 (3 tohit buffs)
I would like to point out that Empathy Offenders work best in teams. The more empathy offenders you have on a team, the better each individual empathy becomes, assuming you follow the correct buffing directions (which I can't seem to find at the moment.)