Unarmed Strike is a simple weapon (PHB 149), so anyone with proficiency in "Simple Weapons" is proficient with Unarmed Strike. Rogues are proficient in simple weapons. So, enjoy that 4-damage punch at full proficiency.
Note that Unarmed Strike is not a light weapon. So, if you want to be a two-fisted pulp hero you've got to take the Dual Wielder feat.
I dunno, that seems unlikely to me. If the Hulk punches someone, it doesn't matter how few feats he's invested, that person is gonna get hurt. And get hurt for a lot more than just one damage.
In Using Ability Scores under Strength, it says, "You add your Strength modifier to your attack roll and your damage ROLL when attacking with a melee weapon ..."
In the Combat section, the bit that says you add your Strength mod to damage appears in a section called "Damage ROLLS," not just "Damage."
Since it's a static 1 point of bludgeoning damage, not a roll, I don't think you get the modifier.
FWIW, I believe the intent is that even a very strong person should not be able to kill the average NPC with a single punch unless the attacker has martial arts (or tavern brawling) training.
Odysseus once broke a guy's jaw with one punch.