My advice is start small and pass to large after redundancy attained. Many successful launches with reusable retrieval permits introduction of nuclear rocket first stage. The advantage of nuclear is 800 sec isp compared to 360 sec isp chemical burn. What is ISPs? Exhaust speed in meters per sec divided by gravitational acceleration. Moreover a volume of liquid oxygen has the density of cement. An equal volume of liquid hydrogen compares to cork. So nuclear reduces the need for liquid oxygen which equates into higher final speed.
The facts about nuclear first stage. If hydrogen used as propellant mass, not at all radioactive exhaust. That is because hydrogen does not have radioactive isotopes. But plutonium exposed to air rusts. That rust is highly radioactive. The nuclear rocket contains the plutonium in a refractory fused metal oxide cylinder which protects exposure to air. So then the biggest concern is full retrieval of the first stage without damage. Hence the emphasis on redundancy. The use of chemical burn launches until the engineers are confident to attempt nuclear.