>>38649
>How those two are determined?
It'd be set as part of the map prior to playing. I'd start with a base value, depending on balance considerations and how many units are expected to exist, and add or subtract based on how wide the border is and the kind of terrain.
>How can one flank?
Attack with numerical superiority on a sufficiently large frontage that the defender can't cover all of it, giving you a positive outflanking modifier. This can even happen on a single province connection, such as 6 attackers vs. 4 defenders over a province connection with a width of 5, that's 5 committed attackers against 4 committed defenders with an outflanking strength of 1.
>Can a province be attacked from several
Attacking from several happens all the time and it'll become more important as a way of acquiring more width.
>one of them designated as the main direction?
There's no main direction, everything turns into total, committed and outflanking strength.
If the attacker wins he doesn't have to move the entire attacking force to the conquered territory, only whichever units he wants to, in that sense there's even more control than an outflanking direction. I'd formalize this as different "Attack" and "Support Attack" orders. Each order is given to a number of units in a province, from the same province some units may move to attack and others to support attack.