Short answers, pulled from the story.
NASA began studying Space Shuttle designs as early as October 1968, before the Apollo 11 Moon landing in 1969. The early studies were called Phase A, with more detailed Phase B studies beginning in June 1970.
A fully reusable shuttle was abandoned because of high cost, technical complexity, and development risk. The fully reusable design required an enormous booster to lift the orbiter, and since cost in aerospace systems tracks closely with mass, the overall vehicle cost would have been very high. The Office of Management and Budget also insisted on solid boosters over liquid ones because of their lower projected development costs.
The Air Force's requirement to launch spy satellites into polar orbit from Vandenberg Air Force Base drove the shuttle toward a larger delta wing configuration. The National Reconnaissance Office also expanded the cargo bay from the NASA-planned 40 by 15 ft to 60 by 15 ft to accommodate anticipated future intelligence satellites. In exchange for these design concessions, the Air Force testified on the shuttle's behalf before the Senate Space Committee in March 1971.
NASA selected North American Rockwell on the 26th of July, 1972. The company's proposal had the lowest cost, the most realistic cost projections, and the design easiest to maintain. North American's experience managing the electrical system failure aboard the Apollo 13 command and service module also factored into the decision.
The Space Shuttle used the HAL/S programming language and the IBM AP-101 as its orbiter avionics computer. The first microprocessor used in the program was the 8088, later upgraded to the 80386.
The Office of Management and Budget insisted on solid rocket boosters because their projected development costs were lower than liquid fuel alternatives at a time when the Shuttle program had many competing elements fighting for limited funds. Engineers at NASA's Marshall Space Flight Center had concerns about solid rocket reliability for crewed missions, and liquid boosters would have offered better performance, lower per-flight costs, and less environmental impact, but development funding was the deciding factor.