Running even a small conference can be enjoyable and very worthwhile, but also complicated, a lot of work, and a big pain in the neck. For bigger ones, you should figure on putting the rest of your life on hold for months before and after, and maybe gambling everything you own. So you need to be sure you really love doing it!
My wife ran academic conferences in grad school, and I'm sure she'd never do it again. An acquaintance of mine runs the annual Hackers Conference, which only has a hundred-ish invited attendees, and at times he's had to dip into his retirement fund to cover tens of thousands of dollars of expenses and beg for donations to bail him out.
Many great conferences grow out of smaller meet-ups. I used to be on the board of directors for the North Texas Irish Festival, which grew out of a pub party in 1983, and had 62,000 attendees in 2010.
If you really want to go ahead with something like this, here's what I'd suggest:
- Start a programmers' club that meets once or twice a month for a talk, perhaps in the evening at a local restaurant with a meeting room so people can enjoy dinner and a beer.
- After you've had dozens of people showing up regularly for a few months and you have a good idea what topics are most interesting, set up a four-hour conference on a Saturday afternoon for your club. Nothing fancy, just arrange a big room with lots of folding chairs, a projector and screen, and some folding tables for people to show off whatever they want to show off. You will quickly find out about arranging speakers, renting meeting halls and equipment, contracts and liability, financing out-of-pocket expenses before anybody pays their entrance fees, and the fact that helpful volunteers are few but many people have opinions.
- If that succeeds and you haven't run screaming into the night, contact Andrew Hutton. He organizes the annual Ottawa Linux Symposium, and can discuss how he runs that very large, sophisticated conference.