Actually, the interstellar version was planned at 40 million tons (256 super tankers) with crew in the thousands. The smalller solar system versions were planned at 10 thousand tons with crew of 150.
Propulsion was never the problem - steering was.
As for size - the larger the ship, the better it worked,
Speed - time to Mars = 3 days.
All versions were planned to lift above the atmosphere before 1st nukes detonated. These were small bombs - the art of designing now lost in the USA.
Motto - Mars by 1965, Saturn by 1970.
Small version cost - same or less than Apollo.
Use wikipedia at your own risk.
Maybe we could buy back the information from the Russians? Kidding. Did we really lose the ability to make tactical nukes?