I might not fully understand the challenge, but Here's an entry with 5 features.
I think the hardest rule to follow is not using two consecutive cuts (combined with the rule that fillets and chamfers are treated as cuts.
In my model I could have done feature 2 (fillet) as only one edge, then filleted the 2nd edge as another fillet feature between the extrusion features 3&4. It would be weird to do so, but would bump the feature count to 6.
Feature count could be further increased by extruding surfaces first, then using the surfaces to remove material, or as stops for up to extrusion depths. SOLIDWORKS does not treat trim operations like a boolean. I'm not sure about other systems.
We should try a few of these and see how they work out. My only fear is it will become an "infinity plus one" situation where each solution is just a bit more complex than the last.