Yes you can at any point after you reach the main city you talk to the inn keeper and select vocation. There are 6 other classes besides the 3 starters. They are either combinations of classes or advanced versions of the first ones.
After that we are going to be running the inaugural GBCER MTG Royal Rumble! It is going to be a Standard event and function with roughly the same rules as a wrestling royal rumble. Two people are going to face off in the first match and the winner is going to progress to the next challenger in the randomly assigned queue. The last person standing wins our lovely GB FNM championship belt. All matches will be single elimination either best of 3 or best of 1 depending on how late the FNM runs.
I think your idea is really cool but that is not how the Royal Rumble works. The Royal Rumble is where 2 wrestlers start in the ring and then another wrestler comes out into the ring around every 90 seconds. Until there have been 30 people who have entered the ring and then the winner is the last man in the match. You win by throwing people over the top ropes.
I honestly don't see how a MTG Royal Rumble would work, lol. If you are going for a wrestling theme I would call it the King of the Ring. That is a single elimination style tournament.