A bunch of questions

[Poulp']

# True or False: Blocking a port derives the enemy of any trade income through that port (only works on ports with dotted lines), but gives you no money. Conversely, blocking a sea trade route gives you some of the money, but does not totally block the opponent'd trade.
# Related question: Is it useless to block ports without dotted lines? Except perhaps to hem in an enemy fleet.

Since I'm on a roll...

Blocking a port, I didn't see any change in my projected income, but a blockaded port can't produce new ships. Clear the seas of Chosokabe ships, block their ports, they are essentially out of the picture.

You've got two means for the same end; crippling their economy. And you can either do it like a hammer, blocking their ports but they will know where to find you. Or play it guerilla-like and raid their sea lanes which can be very long (Shimazu-Date for instance).
Now that I think about it, it is surprisingly subtle.

I didn't blockaded ports long enough to check if they would switch trade lanes. That's actually an interesting issue.