Its a lost cause... and you can spare the money and supplies it cost
If you are playing the AI, and are confident you can hold her off on land during 1861 with militia, cavalry, and irregulars: put everything you can spare into brigs. Start with the Deep South ones, they will get built in Mobile and New Orleans. Station them all in the Gulf Blockade as one big fleet, evade - defend/retreat if engaged. Make sure you send Semmes to join the fleet at the first opportunity. As more come online, rotate any squadrons that fall under 12 strength (or individual ships under 6) back to Mobile for R & R. You should be able to withstand any bombardment without losing ships if you get caught. If that happens, send the whole fleet to Mobile for a couple turns.
I recommend Mobile as a naval base over NO or Galveston. Travel to & from NO can often take an extra turn if delayed, and Galveston will not replenish ships as fast (too small).
The more you have, the more you can afford. By the end of 1861 you should have about a 400-450 point fleet, bringing in @50 extra WS/turn, plus a few $. You will have built every brig available by spring, and can start adding some serious artillery to your militia divisions, which should have trained up to mostly conscripts and regulars by now (or start some other economic development, maybe even throw some resources into an offensive fleet).
This is not a great PBEM strategy.
I wouldn't recommend building extra ironclads unless you are just swimming in $/WS, at which point you have almost won anyway.