I submitted two proposals for LeakyCon, one being an 
“In House Fashion” show where “Yes, there may be a uniform, but they never said the uniform couldn’t be personalized. Be who you are and be proud, but you don’t have to follow “the rules” of appearance, don’t let your house change you…” 
and the second one being “Relations and Relationships: Beyond the Surface” discussion where “We all know that Harry Potter is not only about a boy named Harry who constantly conquered death, it is also about how to deal with personal demons. Thoughts on certain relationships that are either obvious, shared in the community, or things people might have missed. Mainly, will be a discussion on all things Potter but also on real life things…. To help people see that they can get help and it doesn’t always have to be so dark.” 
- “Happiness can be found in the darkest of times as long as you remember to turn on the light.” - Albus Dumbledore”
When will we know who they want to work with for the events and discussion people have submitted?

I believe if they think your ideas are something they want to include, they’d contact you fairly soon. There are a lot of things going on during the 4 days of the Con, they have to have everything scheduled in advance. I’m not sure if they’ll contact you if they won’t be using your idea, which may be a problem. But I’d say if you aren’t contacted by Mid May-June they probably won’t ask you to work. 

Though the best way to get an accurate answer is to email them, I don’t know how the inner workings of how everything is set up works.