i know this may sound like a silly question but when a item or power says base damage +1 per success, does that mean a net roll of 1 success does base damage + 1? or do i need a success to get base damage and from then on it's +1 per success?

The first one. If a weapon has a base damage of 5, it will do a minimum of 6 damage (before soak) on a hit, because you'll do 5 base, plus your 1 success.