I'll just focus on the 50,000 fighters, presumably over the OTL production.
From what i've read each V-2 equals a high performance fighter resource/cost wise, not clear if jets or props. So that's 6000 fighters.
Also, iirc the bombing of 1943-44 cost the germans 18,000 aircraft not produced, of which 14,000 fighters. So that's 20,000 fighters.
However, to actually have a chance to greatly reduce that production loss in the first place, they need to give top priority to fighters much earlier. So problematic or small numbers programs must be cancelled, and production of bombers, at least obsolete ones must be greatly reduced.
So, no 1200 He-177, no 1100 Hs-129, no roughly 2000 Me-210 (this includes the estimated production loss due to the failure of that program), no 1200 Me-410, no 300 He-219. Just going by the number of piston engines, and assuming increased production due to the economies of scale, we get 15,000 piston fighters, possibly more especially if there are some cuts to the Ju-88, Ju-87, He-111 bombers and indeed some other obscure types. So indeed we get quite close to the 50,000 figure.
Instead of Ar-234 more Me-262 are built. If 6000 V-2 equals 6000 Me-262 that would dramatically change the air war picture as well.
So, 50,000 fighters means much heavier losses to US/UK bombers which indeed might cause the raids to stop altogether for a period, less damage on the ground (hence less disruption and more production for prop and jet fighters), less damage to oil infrastructure so more oil produced and available etc..
As to R4M rockets, how many R4M rockets can be built for every V-1 and/or for every Me-163? There were 30,000 V-1 built, so if 10 R4Ms can be built for every V-1, that's 300,000 R4M rockets, though that might be too conservative. Perhaps say 500,000 is more realistic. By the same metric, if we have the 6000 V-2s converted to R4Ms instead, considering that it cost about 20 (!) times more than V-1 to built, then that would be 6 to 10 million R4M rockets, so we actually got to the number in the OP. However, for the rockets to have an impact they need to be ready 1 year earlier.
So all in all, it seems doable with an early enough POD. The downside of no V weapons means the fighters used for air defence over UK would be mostly used over Europe, i'm curious how many, probably a few thousands? Same about the AA guns.
However with so many extra german fighters means there is likely no D-Day in 1944 in the first place, as there would be no air superiority. In 1945 maybe they could try an invasion, but by that time the germans have a lot more jets ITTL, plus high performance piston fighters like Ta-152. It will be in this scenario that the B-29/nukes would be seen as the last chance to do something about an invasion, BUT i would think an R4M equipped Me-262 would eat B-29s for breakfast. Same as the Ta-152H. Considering the small numbers of nukes, would they even survive interception from either day jet/prop fighters or night radar equipped jets/props to drop the nuke on a german target?
So probably in this scenario the nukes might actually be used in Normandy to clear the way for an invasion because it's a lot closer and they can be protected by literally thousands of US/UK fighters.
) that hitler's government would bring the US into war against Germany no later than June 1942. This would delay the start of the Manhattan Project, but not the influx of refugee scientists thanks to the immoral and idiotic racial policies of hitler and his minions.
