Black Flag (2013): abilities and upgrades
With the original Black Flag, I wouldn't think about progression the same way as Origins or Odyssey. You're not putting skill points into a big character build. You're getting tools through the story, buying better equipment, crafting upgrades and improving the Jackdaw.
Health first if you're struggling. More health gives you room to make mistakes. After that, look at what you actually use. If you're always running out of darts or pistol ammunition, carrying capacity is going to help more than buying something you barely touch.
Pistols are useful, but capacity and reloading matter. More holsters let Edward carry more loaded pistols for consecutive shots. That doesn't mean an endless magazine. Go into a difficult encounter loaded, and don't start the four-kill pistol challenge with half your weapons empty.
The blowpipe changes stealth. You get it during Sequence4. Sleep darts temporarily remove a guard without starting an ordinary sword fight. Berserk darts turn a guard into a threat to the people around him. Those are different jobs: use sleep when you want a quiet opening, and be careful about causing a fight when your objective calls for restraint.
The rope dart comes much later in the original. It's a Sequence11 unlock, not an early-game purchase. It lets you pull enemies and perform hanging attacks from suitable elevated positions. If a guide says you get it in Sequence3, check whether you're reading about Resynced.
Don't forget ordinary stealth. Look at patrols before moving. Use cover and height to choose your approach instead of turning every restricted area into a sword fight. Having a better weapon won't rescue an optional objective that specifically required you to stay unseen.
Keep Edward's upgrades and the ship's upgrades separate. Crafting a better pouch doesn't improve your broadside. Buying stronger shot doesn't give Edward more health. When something is giving you trouble, work out which system is actually failing before spending your money.
For me, the useful order is simple: fix whatever keeps getting you killed, increase capacity for the tools you're using, then buy the upgrades that open up the way you want to play. Appearance changes can wait if you still need the practical stuff.
Black Flag (2013): abilities and upgrades
· Games / Assassin’s Creed IV: Black Flag