ok ...fair enough ......
Do you allow the A6M* RD factories convert to production or do you take the repair hit and convert to another research leg ?
On to Question #3 ....
George (IJN) and Frank (IJA) are also desirable rides but neither have predecessors for research so guessing no real good way to accelerate
Obviously, there will have to be some hard choices as to what and when to RD ...
I realized I never answered your question. Most JFB agree that you want to focus your R&D on Fighters and that the R&D of the Frank is vital. JFB's are somewhat split on the value of the Sam versus Jack/George. In any case, the minimum number of r&d factories you want to put on the Frank is 5-7 x 30 R&D factories and many JFB's do numbers in the teens. There are three r&d factors in play here.
1. There are diminishing returns on R&D factories, especially given the engine bonus. Your nth factory that is actively doing r&d on an aircraft is only going to reduce your arrival time in proportion to 1/(2n). When you get to 7 or 8 repaired factory, that 8th or 9th r&d factory is making only a few days difference in your arrival date.
2. R&D factories repair at different times - there is a huge random element to it. So if you have 7 and the RNG hates you, your arrival date will be later. If it loves you, it will be early. The more r&d factories you have, the more chance you have to get a significant number of them repaired before your anticipated repair date.
3. The Engine Bonus - if you have 500 engines in the pool, you can double your R&D output at each factory each turn for the cost of 1 engine per factory. If you are going to R&D the aircraft, you probably want to have 500 engines in the pool a couple months before the anticipated repair date. The more factories you put on it, the more mandatory this is.
As a general rule, my impression is that most JFB's decide how many aircraft they want per month and divide by 30 to get the number of R&D factories they want to expand. If you want 300 Franks per month, go 10 x 30. If you want 150 per month, go 5 x 30. etc. Japan produced 13,811 fighter in 1944 alone. That's ~1150 per month. Plan accordingly.
On the Sam versus Jack/George: It is definitely a good carrier fighter, but by the time it could arrive, I do not expect to want to pursue a CV battle. Just as AFB's avoid CV battles in 1942, I avoid CV battles in 44 and beyond (assuming I even have any left). If you beach/rebuy your CV air groups and have PDU: On, you can replace the Zeros with the George and the Jack. The Sam is still arguably better than the George and the Jack in most roles, but the margin of superiority is thinner than versus any of the A6M models and the arrival date of the Jack/George is 2 YEARS sooner. This allows you more opportunity to accelerate and makes your IJN fighters more competitive at a time they are facing the Corsair. If I'm replacing Zeros with the Sam because I expect to have the CV's or PDU is Off, there is no contest. You almost have to go big on the Sam. If go big there, you need to scale back on the Jack/George to compensate.
In the end, you have to spend supply to build up your R&D factories and your engine factories as well. You can't do it all or the supply shortage you create will give the advantage you have in China to the Allies everywhere.
DO NOT DO THIS AT HOME TECHNIQUE
Finally, there is a technique that you can choose to pursue 1 late war model that takes point 2 above to an extreme. Expand a massive number of r&d factories: like 30-50 x (30). It will cost you a LOT of supply just for the expansion: 50 x 30 x 100 = 150000 supply just to expand. As factories repair, you will notice that a few repair to 2 x (28) while most are still 0 x (30). Later still, you will have a few that are 3 x (27) while others are still 0x(27). Those 3 x (27) and 2 x (28) are likely to be the ones that would repair early rather than late. Note I say likely, not guaranteed. As time goes on, you would prune out the factories that have repaired fewer devices and keep the ones that have more repaired devices. This can potentially buy you a couple weeks or maybe even a couple extra months on arrival date, but the cost in supply is extreme. Please note that I say CAN, not WILL. The RNG is a fickle bitch - all you can do is try to slant the odds in your favor. I'm skeptical that it is worth it, but it improves your chances of getting your R&D factories repaired well in advance of the estimated repair date. Along the way though, you will waste a LOT of supply both needlessly repairing factories and doing expansion you will never/only temporarily use to build the aircraft.