You're going to need a complete game design document that outlines the entire scale of the whole project. (The fighting system (e.g. 4 buttons or 6 buttons), how many characters, what their moves will be, their endings, how many stages, game modes and features.) Once you have the vision of what you want, then you can move on to hiring people and directing them to the tasks you want completed.
Maybe have a journal that explains the whole project and a sketch or two to sell the image and hype people up. If you hire free people now based on a whim, they're going to have nothing to do because there's no game design document or direction to follow, and lack of work means lack of engagement. That lack of engagement is what loses people.
I'd suggest approaching an indie project group and asking them questions. You'll get better advice from folks that have made games or finished their projects.
A pitch is a good idea too with a defined scope, and even a tentative timeline. It shows some planning has gone into the game. If this is a passion project meant for 'free'. The amount of expertise you're after won't come easy. Most folks that specialise in that kind of work charge per hour, or are already involved in other gaming projects. If you don't have a budget you'll struggle to get them interested. It might be an idea for your friend to ask around in their classes for help. If they're studying the same things, they might be interested in helping out. Could be good for course credits or even as a degree's final project.
Start small. Forget a big game. Make a small achievable prototype that could be made into a 'big' project at a later date. It'd be best to have an idea that can be expanded than nothing at all.
Also considering you're only able to do the project 'casually' in your spare time. The timeline for completion will be long. Most folks that might be interested are likely to be only available casually too. They might drop out as well at a later stage or even early. If they're artists doing commissions, they will likely prioritise anything money-making before your project. So you might get gaps in team members anyway.