Good questions, El Capitan!
For any beginners reading this who haven’t read Don’s essays, the shuck-shuck technique involves building two (or more) fleets of transports that can repeatedly swap places with each other to deliver a steady stream of ground units across an ocean to the front lines. For example, if you have an American fleet off the coast of Eastern Canada, and another American fleet off the coast of France, the American fleet that starts in Canada can deliver American troops to German-occupied France, and the American fleet that starts near France can return home to Canada so that it’s ready to make a delivery next turn. In theory, this is much stronger than just piling up transports for a one-time delivery, because if Germany manages to repel your initial assault, then they will often have a lopsided pile of high-value troops in the contested zone (e.g. mostly artillery and tanks) that you can then immediately attack again, at a profit, before Germany gets a chance to feed in additional defensive infantry. It’s usually easier to wear down Germany by attrition than to come up with a stack that can wipe Germany out in one fell swoop.
In my opinion (and I think most of the regulars would agree with me here), the shuck-shuck is still quite useful in 1942.2, but it is not nearly as powerful as it was in Original or Revised. The problem is that there are no high-quality shuck-shuck routes that touch the Eastern United States. From New York, you can only shuck-shuck to Morocco or French West Africa. Those can be useful delivery spots for turns 1 and 2, but you rarely need to make repeated deliveries to Africa. There is one strategy for long, slow games that involves marching American troops on land from Morocco all the way to Persia, but it usually won’t come up in beginner games, which tend to be faster and more aggressive.
What most 1942.2 players do is march their troops on land from the Eastern US to Eastern Canada, and then run the shuck-shuck out of Canada. Relative to A&A Revised, this slows your shuck down by one full turn, since you have to build the units in the Eastern US, then walk them to Canada, and then ferry them the turn after they reach Canada. From Sea Zone 10 (Newfoundland / Prince Edward Island), you can shuck-shuck to your choice of Norway, NW Europe, France, or Morocco, which is pretty good.
Assuming you want to use the Eastern Canada shuck, there’s no fixed number of transports that you need, but you want to think about what your goals are. Are you just trying to be a nuisance, e.g., take Norway for the income and force Germany to either give up that income or waste a couple of troops re-taking it? You can probably do that with as few as two total transports (one in each fleet), assuming you have a loaded carrier available to provide air support. Are you trying to take and hold a major territory like France, so that Germany can’t take it back from you? You need as many transports as you can usefully fill. Assuming America is collecting something like 40 IPCs, that means you can fill about 5 transports a turn – for example, 6 infantry, 3 artillery, and 1 tank will cost you 35 IPCs. So, for that shuck, you’d want a total of 10 transports – 5 in each fleet. You want to leave at least some buffer in your income, i.e., don’t bother building an extra transport if you’ll have to commit 100% of your income to fill it, because then it’s too easy for Japan to ruin your shuck by forcing you to respond to a threat in Alaska, Hawaii, etc.
If you see that Japan is threatening American territories, it usually makes more sense to plan on a 4x4 shuck (8 transports) or even a 3x3 shuck (6 transports) so that you can build infantry to defend the Western US and still invest in the occasional sub or fighter for the west coast. Similarly, while you are purchasing your fleet of transports, you will need to have more modest goals. E.g., if you are buying 2 transports a turn for 14 IPCs, that only leaves the US with 26 IPCs to buy ground troops, so you can only fill about 3 transports per turn while you are ramping up.
Defending against the Luftwaffe and killing the German Med fleet are two different objectives. You really want to kill off the German Med fleet with the British air force sometime in the first three turns unless your opponent goes crazy and buys multiple additional ships for the med (not recommended). If you are only fighting the one German battleship, you can probably kill it with something like 1 bomber + 3 fighters. So the German Med fleet should be introduced to the sandy part of the Mediterranean seabed well before American ships can arrive off the coast of Rome.
The Luftwaffe starts off with 6 fighters and 1 bomber. To defend against that starting air force, you don’t need a huge defensive fleet – 1 carrier with 2 fighters, 1 battleship, and 2 destroyers should be plenty. Unless you are defending an enormous stack of transports (e.g., six or more), it’s usually OK if the Luftwaffe trades off evenly against an American fleet. The Germans need to keep at least some planes available to fight against Russia, so if they lose their entire air force over the Atlantic, that will buy Russia some critical extra turns, during which you can rebuild the American Atlantic fleet.
If Germany builds extra planes (it’s not unreasonable for them to get as high as 8 fighters and 4 bombers), then you’ll need more defense. In practice, this usually means combining the British and American fleets. You can do that by building a new British fleet and then quickly moving the American fleet on top of it, or by building British carriers and flying American fighters onto the British carriers. Sometimes it helps to build off the northwest coast of London, because that can be out of range of German fighters. It’s a relatively safer place to build, and then once your fleet has enough defensive firepower, you can move it into the Channel or the Baltic Sea to cover your transports during an amphibious invasion.
India usually doesn’t see much of a role in an Allied shuck-shuck, although sometimes Japan will use a shuck-shuck to move infantry from Tokyo to Yunnan (only 1 fleet needed) or Burma (2 fleets needed, but it’s immediately adjacent to India).