All else equal, no they won't be as big as a single could have been, but they'll be well more than 1/4 that, and when topping for four of them, they'll resemble a main cola a hell of alot more than they will a nug..
About your other questions, anything above the snip should grow as if it was unsnipped.. At the tip of any shoot, auxin is created, and it travels downward, telling the plant to dedicate its resources to growing tall so it can compete for light in nature come flowering time.. Snipping the top cuts off the auxin supply, and cuts off that message causing the plant to grow bushy instead.. But each new shoot will have a new supply of auxin and tries to act as if its the only top.. If you snip those, you can follow the downward path and see what 'might' be affected, but results won't be as predictable/uniform.. Those are the gems of UB's technique..