Hosting a Regional Meeting is an easy way to learn the ropes for hosting an Annual Conference. Attending lots of HAPS Annual Conferences is another great way. And hosting is not you out on a limb - you get plenty of support from HAPS!
For a Regional Meeting, you can generally expect about one hundred participants most of whom have arrived from driving distance for a one-day event. Some regional meetings last a little longer by including another half day, but that is up to the organizers and the facilities. Your site must have room for breakout workshops and a larger hall for keynote speakers. Take a look at the Regional Meeting Online Application for more information.
For an Annual Conference the expectations are higher. Your institution will need to provide 15 meeting rooms of various sizes as well as a place large enough for 500 or so participants to get boxed lunches and eat them. You will also need to be located in a city that has relatively easy air access to the rest of the US and Canada. If that sounds like your institution take a look at the Annual Conference Online Application for more information.
Want to talk to a human about this? Contact the Chair of the Conferences Committee.