I'd tend to favour fewer rather than more, which seems likely to feed the fish off and reduce the odds of a pick-up. Funnily enough, just read Trefor West's - he's been a barbel guide,as you probably know - book on barbel.
He's adamant that a dozen baits in the water will be detected and investigated by any barbel within 40 yards. Pellets in the summer; meaty or pellet paste wrapped around pellets for more leakage in winter, with the freebies baitdroppered in or in PVA bags. He says 90% of his barbel are caught after unstruck bites from chub, and come from swims with the same pace in winter as the barbel live in in summer, often a few swims downstream. Twenty minutes in a swim, he claims, is enough to get a bite if there are barbel present.
There's some interesting stuff, too, about fishing upstream, to keep the bait in the line "fed"by the leakage that the barbel hopefully home in on when you tweak the bait back downstream.
I'd gone off barbel fishing, and the barbel fishing near me has gone off too, but the book whets your appetite.