If I start something myself, what are the key indicators that the project will be successful?
There are not always concrete markers to tell if an event is going to be an amazing success.
The thing about running an event means that even if the event itself does not turn out the way you wanted it to, you have almost certainly learned a thing or 2 about event running that you can take forth with you to next time.
Whether you are feeling confident about your event or not, remember that this is your chance to make the most out of your opportunity and show a diverse range of skills.
Just because your event may end up having poor attendance in the end, there are heaps of things that you can emphasise on your application, such as your skills at co-ordinating speakers, trade stalls, fundraising, or a team of helpers. There are many metrics by which you can measure success!