Illuminations is very easily seen from all around the World Showcase lagoon. Thus, while getting a table at Rose & Crown to watch it from would be great, I wouldn't worry about that too much. If you have dinner somewhere in World Showcase, you can wander out to the lagoon about 15 - 30 minutes before the show starts and still get a good spot to watch the fireworks (I know some people stake out spots an hour or more ahead of time, but on our recent February trip, I never found that to be necessary).