Between 1945 and 1947 the US only developed 12 additional bombs to the 5 they produced in 1945. This very limited expansion of the US nuclear capability was not due to technical limitations, it was due to a desire to contain nuclear proliferation, and a general demobilisation following the outbreak of peace in 1945.
In 1947-8, with the cold war rapidly escalating the US quickly ramped up its nuclear arsenal. SAC stockpiled over 133 bombs in less than 18 months.
I do not know if there were additional facitlies developed for production of the necessary fissile material, but the change in American attitudes to a nuclear buildup was very rapid, and I dont see any reason why the same could not be done in an extended war with Germany. If the war had progressed into 1946, I dont think it implausible to speculate at least 100 bombs in US arsenal by the latter part of that year.
In 1948, General le May, then head of SAC developed the plan on the use of the nuclear arsenal. Essentially over a seven day period it had been planned to swamp the Soviets with over 150 bombs dropped on 70 cities within the USSR. This plan was repeatedly changed and repeatedly updated, as the threat evolved, and capabilities increased
I dont see why the US would not apply a similar strategy against the Germans. The Americans had no qualms about using WMDs in Europe against her enemies. the fact that the post war enemy was the USSR and not germany is irrelevant. My opinion, the US had the capacity to build abombs on an industrial scale by the end of 1945. They would be likley to have 100+ bombs by the latter part of 1946. They would be likley to use such an arsenal enmasse on a recalcitrant Germany as they planned to do against the Soviets if the need arose. The long term radiation effects were not that well known (I understand) and were of secondary concern anyway
Germany under the hail of 100 or so atomic bombs is a nuclear desert. The average casualties per bomb in Japan from August 1945 through to end of the year, was about 400000 per bomb. If 70-100 bombs were dropped on Germany the expected casualties could be as high as 28-40,000,000 million. All the major centres would be wiped off the map. The moral dilemmas this might pose are enormous and unthinkable, but I doubt that would have stopped the americans if they felt they had to resort to nuclear weapons. By 1948 they were quite prepred to undertake such a program against heir enemies, if the need arose.
Given the right incentives, such as a prolonged war, or use of WMDs by the Germans would IMO have given the US the casus belli to carry out such a policy.