Not going to get a number... tents, tires, awnings, water, cases, all pretty common items. Send us an email if you want to discuss your specific use case thanks!
With the exception of the towers being all the way down, how much of the roof rack weight is resting on the center bolt (1/4-20). I am curious as to why not create 3 sets of 3 holes in the towers that line up with on another, three on each side and the 3 in the middle, since in the end the adjustments has to be made to line up one of the three holes in the middle.
almost no weight actually rests on those 1/4-20 bolts. In the end the most I'll use those center bolts is in front, usually when a light bar is added, other times a better gap with the fairing can be achieved by going lower and being halfway between 2 of the holes. The only time I'd use bolts elsewhere is if trying to lift the back of the rack up higher, like to fit a table slide-out, which wouldn't happen on a GX460 anyway as there's an antenna in the way. Are you suggesting 3 large slots all the same size, so 3 of the 3/8-16 bolts? that's actually not a bad idea...
Varies a little depending on options but most complete Expo++ racks are $1100-$1200.. including the one shown in the video here. send an email sales@gamiviti.com for a more detailed quote thanks!