The basic design of the A4 engine in the V-2 was a sound concept. The reliability of wartime production was held back by the deteriorating conditions and post-war testting was held back by the aging of the captured components. The US and UK used nothing but captured parts, preferring to iterate on the original design rather than build new components for an old rocket.

The US took their testing data and combined it with the fruits of Operation Paperclip's R&D to create the Redstone program. The Rocketdyne A7 engine was a direct successor of the A4 and was reliable enough to put the first US astronauts in orbit during the Mercury-Redstone program.

In short, an A4/V-2 would have been reliable enough to serve as the foundation of a British space program as long as it was built to spec without the material substitutions carried out due to wartime shortages.

What is too many? Same could be said of flight, or steam engines, or probably ancient seafaring canoes. As long as folks keep volunteering, its not too many.