Oh. When you said
]I don't know about the actual system for it or any of the problems I should expect to face.
I thought you meant you had a system in mind, but had never played or run it before. My misunderstanding. Freeform is very much viable, particularly if you've never played a system game in RL or on the internet
Okay, first decide what kind of group game you want. There are two major categories here, though almost all games will draw on both types.
-A plot-driven game will be primarily dependent on the GM. If the premise is a group of heroes on a noble quest, or the Mystery Gang exploring a haunted mansion, this will involve the GM presenting situations, problems, or events and letting the players react to them. This requires the GM to be much more committed, but also has the benefit of needing less preparation and pre-planning, as you only need to react to what the players are doing right then, as well as having them tend to be in one place (though there are exceptions).
-A player-driven game (what systems often call Sandbox) is dependent primarily on the players taking initiative. This tends to require more active, involved players, but less work on the part of the GM. The GM sets up an environment, anything from an exotic hotel resort to a space station, dumps the players into the environment, and then lets them create their own stories and situations by interacting with each other or the environment. This has significantly more involvement than a plot-driven game initially, but much less once it gets off the ground.
One thing to consider immediately is the notion of 'your character'. As the GM, every character that isn't a player is technically your character. You might have a specific character who does the most player interaction - the captain of the spaceship they're on, for example - but avoid the trap of seeing an NPC as 'yours' any more than another.