A fuchsia in the garden would easily get to that size but it usual in baskets to pack them in and keep feeding. I never have the heart to do it so my baskets tend to look a bit sparse but I think most folk would put at least three in there.

I wouldn't - I'd just use one upright fuchsia and the rest of the plants would be trailers (lobelia, surfinia petunia, million bells, whatever). You've always got to have an 'upright' in the top... If you're using only trailing fuchsias to make a display alone, then 3 minimum.

I have quite a few Easy fill hanging baskets if you are doing a mixed basket I would use a least five plants in the top of the basket but you do have to watch what you are planting the most vigorous plants will tend to take over the basket if you look a my pictures there is an Easy fill basket filled with begonia apricot shades that was grown from plug plants and I do the same with Fuchsias using only one variety I think this is the easiest way to get a balanced basket.
But if you do a mixed basket and get it right it can look spectacular add moisture retaining gel to you basket this also helps I find the 14" Easy baskets tend to catch on the walls when windy.

Thanks for the help everyone.