The unit cards show the total number of guns, it does not relate what size of gun nor which are fore, aft or broadside.
One important statistic that is not readily available in the game is the total damage output of each ship's broadside. Distant port blockading only prevents the trade originating from that port returning home, so the financial benefits need to be weighed against raiding the trade route for income. Home port blockading is therefore high risk and either performed by solo fast ships which are expendable or large enough enough force to make the blockade permanent. The impact of blockading is often significant enough to justify sizeable home fleets for defence. The most vulnerable end of the trading route is a faction's home trade ports as it prevents all trade from arriving, especially early in the game when they may only have one trade port.
Blockading a port does not prevent naval recruitment, but if the port is unoccupied and your forces raid this will damage the facility and prevent recruitment. However, unlike commerce raiding no income is earned by the blockading. Blockading a trade port prevent all trade through the port so it is very effective, and if the port is unoccupied it is raided and damaged.
