According to the wiki, there are 4:
Supported by the rebuilt Liberty Prime, the Brotherhood assaults the Institute and blows up its reactor. For the player character's service, Elder Maxson promotes the Sole Survivor to the highest rank of Sentinel.
The Institute is infiltrated and destroyed, sparing the Commonwealth of their oppression.
With the help of Deacon, Tinker Tom, and a stolen vertibird, the Sole Survivor infiltrate the Prydwen and destroy it from the inside, causing it to crash. Later, the Institute is infiltrated and destroyed. The two organizations most opposed to Synth freedom are eliminated and the Railroad can continue its work in relative peace.
The Institute and the Sole Survivor attack and eliminate the Railroad. Later on, with the help of Institute synths, Liberty Prime is hacked and shoots the Prydwen out of the sky. After returning to the Institute, the Sole Survivor has a heart-to-heart with Father and assume his position after he dies.
There are 78 permanent SPECIAL points in Fallout 4.
- You start off with 28 points.
- You can find a You're SPECIAL! book in your Sanctuary home for another point.
- Can only increase a maxed stat if a debuff like alcohol is used to temporarily lower one of your maxed stats
- You can train all your SPECIAL stats up to 10, so that's 42 remaining points.
- Additional Bobbleheads (for each specific SPECIAL stat) can be found, 7 points.
You can max out your character with 10 in each SPECIAL trait provided every time you level up you simply choose the appropriate training to increase your stats (as opposed to choosing perks).
Remember, there's no level cap, so you can keep on levelling and start getting other perks later.
So you start off with 28, but you can easily improve all of them to 70, should you choose to only train those perks starting at Level 2.
This means 70 - 28 = 42. Meaning the earliest you could max out all your stats is getting to Level 43, while every time you level up putting points in the stat you want to increase, provided you also don't find any bobbleheads along your way.
Additionally, some perks grant permanent increases in stats at specific times of the day or at a certain HP level, so those are technically also "permanent".
Best Answer
Well, let's put the speculations aside and test it experimentally!
If we compare two identical stock double-barrel shotgun (With a long barrel) in our inventory, we can see that the predicted damage for the shotgun with Two-Shot is already twice the damage of the standard shotgun:
If we test it point-blank on a gentle Deathclaw, we can observe the real damage difference between the two shots, which is just over 2x:
The slight difference can be explained by the pellets spread. I tried to reduce it to the maximum by using the Long Barrel mod and having my character placed at the exact same spot, doing a Body shot in VATS
So, in conclusion, Two-Shot will fire twice the amount of pellets from a shotgun doing correctly twice the damage.