Yep every turn you need to hit good/great/perfect, it's the reason people consider G3/Log teams kinda stressful as a single mistake can ruin your entire run.
To get an idea how different captains stack you can always use the damage calculator:
http://optc-db.github.io/damage/#/
Usually people use a captain + friend captain with the exact same ability. There's a few LOG users on gaf you could befriend for Log luffy friend captains.
It's possible to mix log with various STR teams/captains though, as long as their captain ability has synergy.
(you can't mix LOG with G3 for example, as they have mutual exclusive activation conditions)
No, every damage buff in this game is multiplied, that's how you get the huge numbers (like 4 million damage).
2 Log Luffy cap skill (4x4 on the last 3 hits) = 16
Then you have the chain multipliers which on the last hit is x2
Then the perfect multiplier 1.9x
Then the ship damage buff 1.5x
The type modifier (x2 if advantageous or 0.5x if it isn't)
that's a lot, but there is more, then you have the type/class buffs and the orb boosting buffs.
So for example a log luffy team in a perfect scenario could possibly deal something lke this on the last hit:
16x2x1.9x1.5x2x2x2 = 729 times the character's attack.
Wow thanks a lot. This explains why my damages vastly differs from time to time. The multiplier can go up to hundreds.