We went to Gospel Brunch on our last visit to Orlando. My wife works for Live Nation (who owns HOB) so we had comped tickets but we saw people purchasing tickets at the box office on the morning of, so you could probably do that. There will be some shows that are sold out so to be sure you may want to call HOB a couple of weeks in advance to insure your spot. HOB is not Disney-owned or operated so you will need to purchase directly from them.
The show was pretty good, very interactive...The food was the highlight though. It is truly a brunch to behold. A huge selection. They had just about everything you could think of from all of your basic breakfast items (including a custom-made omelet station) to some great lunch choices including prime rib (cut to order), awesome jambalaya, salads, deserts (white chocolate bread pudding and peach cobbler, cookies, cakes, etc), etc. You will certainly not leave there hungry.
They have two shows, one about 10:00 and one about 12:30. Each seating (including the show), lasts for about 1.5 to 2 hours. We went to the 10:00 show and one word of advice. Depending on what time of year you are going, it can get a little chilly in the music hall (very large) so I would bring a sweater for the early show.