Fredericksburg Convention Center is a bit smaller than Dulles at about 125,000 sq. ft.
https://www.fredericksburgconventioncenter.com/
The dropdown 'about' on the right has specs and floor plan. The ballroom would be good for the autograph signings.
It is not a bad space. It is in the back of Central Park which you pass on Rte 95. For perspective it is directly behind the rest stop on the southbound side of 95 just before the Rte 3/Plank Rd exit. There is plenty of parking in their lots and the Fredericksburg Nationals stadium which is next door. It is also walking distance from 4 hotels; 3 Hilton properties (Hampton Inn, Hilton Garden and Homewood Suites) plus an Extended Stay America. There is also a Clarion and Comfort Inn less than 1½ miles away on Carl D. Silver Parkway which is the road that takes you to the convention center from Plank Rd.
The food selection within one mile is extensive. From fast food to sushi, Mexican, Japanese and Italian.
The downside: The drive down Rte 95 on a Saturday after about 10 am can absolutely SUCK! When I lived in Springfield my wife and I would turn around and go home when there were things we wanted to do in Fredericksburg, but did not want to deal with the traffic. Most of the time Rte 1 can be better as the traffic lights break up the traffic, but if there is an accident anything goes.
Full disclosure - I live 150 yds off of Plank Rd 6 miles to the west, but that does not mean I would attend the show more often than I do now which is once every few years.