Set up a real convention is a HUGE task. If you would like to know more about it talk to a convention staffer or Chair. They have meeting and conventions just to learn how to set one of these things up. There is a lot of legal stuff and regs you have to go through.
Pick any well run convention and email someone on staff. They should be able to point you in the right direction.
I've been going to cons for a good 6 years now. Mostly sci-fi and furry. Been part of security at the last con I attended.
Forgot to mention I also do Steam Punk. But that convention is a three day outdoor event. So it's not connected to any one hotel or convention space. Unlike a normal convention the steampunk event has no badges. Most of it is free to anyone. However special events like concerts and demonstrations require tickets.
Things I do know about conventions.
It's best to set up a non profit first. You will need a staff of people. Best to have a layer on board as well.
You will be required to rent the convention space. You will also need a 'room block'. This is the number of hotel rooms you guarantee will sell derring the event.
You will need to provide security. Not just volunteers. Wile volunteering at that furry con I was made aware there were two vested and armed officers and an EMT unit. Needed because of the high profile people that attend these cons. I had dinner with a retired US military officer, an astronaut, a comedian, a guy who draws comic books for a living and a few other high profile people. It was a blast.
Expect to be in the red the first few years. It takes time for a convention to grow.
I don't mean to be a wet blanket. Just wanted you to know a bit of what it takes to through together a convention.