Your 18-55 is plenty sharp enough as long as you have flash to work with. With its fairly small aperture as the largest, focus accuracy is not as critical due to greater depth of field. Exposure is actually easier to be consistent shot to shot on Manual mode for all Exposure Triad values provided you have a TTL flash. Even if you have only a full manual flash, dialing it in for the distance and exposure settings, pretty much can be left along after setting power. Over exposure can occur with closer subject distances than those where your test shots suggested a power setting. To prevent the Flash look, some sort of bounce card or a white rear wall or a diffuser like the Gary Fong Lightsphere can work well.
When shooting a group of people, it is usually best to move back so distances between the people don't cause big differences in exposure.
Flash and effective use of it is the great equalizer in cameras and lenses. Low light events where flash is not allowed is where higher end lens come into their own.
During diner events, you have more leisure time since after meals are served it is not a time to take any photos and the only time it is appropriate is during toasts so you have some off time. With weddings, there is no slack time so they are some of the hardest events to cover well. Starting with home shots getting prepared, shots of departing home, guest arrivals ceremony, reception, parties, catching enough free time just to use the restroom is rare. So if you survived a formal wedding with its 20 hour days, a charity event would be a sleepwalk;>)
One of the most beneficial results of using flash and all manual is it speeds up post processing time a great deal because there is more shot to shot consistency. For non-flash events, all manual except Auto ISO can do almost as well.
Good luck on your second event.
