[Nemo]

The biggest thing you need is a bunch of volunteers.

What type of FTC event do you have in mind? How many teams?

Here's a quick list of some of the big items you need:

Volunteers (key volunteers can be tough to get)
Venue (competition floor + stands, pits, judging areas)
Various tables in the venue (pits + field tables = 30+ tables)
Volunteer food
Concessions
Fields (including practice field)
Field electronics + laptops

Whether this is doable for you depends largely on the volunteer situation. When we were doing qualifier events at our school, we'd have over 50 volunteers for a 20-24 team event. Now we're on league meets, so it's a lower number. Getting enough referees and judges is challenging. Getting an emcee can be challenging. You also need a head FTA, and lead HW+SW inspectors, and you need people who know what they're doing in those roles. Each of those key volunteers needs helpers. Then you need a variety of non-trained positions such as field reset, queuers, pit runner, pit admin, and check-in.

Venues can also a challenge, because basketball seemingly takes over every square inch of gym space for every minute of the basketball season.

We have a lot of volunteers in our area, and hosting the event at the school made a lot of things free or inexpensive. That makes it pretty doable here. The first time anybody hosts an event, it's going to be stressful and a learning experience. But once an event has some momentum, the event capacity goes up for the program in your area, and that's a beautiful thing. Somebody's gotta do it.