Advantage of 4 engines. Engine failure on take-off only requires consideration of loss of 25% power compared to 50% loss for 2 engine aircraft. The principle was that this allowed a higher take-off weight. I am sure there are many other issues, like 4 smaller underslung engines allowed shorter undercarriage, but offset by outboard engines further to rear on swept wing aircraft during take-off rotation and also max bank on touchdown.
JATO interesting except that transport, storage, handling, training and time expiry were added expense for limited advantage.