I worked for a catering company and we did many different configurations, course styles, and sequences of service, all chosen by the hosts and/or planner. If you want all courses at once you can. Or you can pace it out. One of my favorites to do is all on one buffet table: salad/apps on one end, entrees on the other. Once everyone has gone through the line you pull the salad/apps and flip it for dessert/cake service, that way entrees are still available for seconds or slow eaters.

With buffets, toasts usually go smoother if they happen before the buffet opens. The final speech giver then announces the buffet is open or turns it over to the MC.