I think that you are confusing a couple of things here. There is stopping leaks on one hand and taking in a massive amount of water at one time if you got seriously knocked down or pooped. Neither is a good thing but obviously the latter is a really serious problem, the first is more of a serious annoyance. You can't fool around with taking on a bunch of water since that could be sinking issue. To my mind, whether you have doors or dropboards they need to be very strong and installed in such a way that they can't fall off or come open if the boat is doing nasty things. It does not help if you have immensely strong dropboards if they are not there. I think doors are better but boards are doable as well, although not as convenient for their main purpose ie entry and exit. We have doors but can also put our old dropboards in behind the doors when conditions warrant (which is very rare).
Stopping leaks is a very good thing and someone suggested a pressure washer to test for leaks - good idea but don't get the nozzle too close or you damage bedding.
As for cockpit volume, if you were concerned and plan to have some jerry cans with you (which is almost a necessity because many places you go you need to dinghy water and/fuel to the boat since there are no marinas and fuel docks (one boat in America Samoa went to the fuel dock used by the fishing boats, some of which are 150'+ - and blew out the manifold system connecting his fuel tanks. You can imagine how much of a mess that made).
Anyway, you might be able to position some of the tanks inside the cockpit, rathen tied to the rail where they are more vulnerable. Takes up volume but you need to mount them very solidly so they don't just float up if there is water in the cockpit. Also, don't get too carried away with filling up all of your cockpit. For example, it is safety issue to be able step up from the cabin and move into the cockpit into a secure cockpit. If all the foot space is gone and you climb up onto the seats that is a potentially awkward position. Also, picture how you will be sitting in the cockpt and moving from the cockpit to interior and onto the deck and imagine where you want to put your feet and legs for ease of movement and comfort.
Finally a question, I think you said you had 6 scuppers for drainage - are they in the cockpit well or at deck level - how big are the hoses/passages from these?
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.