Can even a little gum bleeding during flossing indicate gum disease?

NO. A little gum bleeding during flossing may indicate improper flossing technique. Floss cuts into the gum and causes an injury which termed stillman cleft. Press the floss to either side of the teeth prior to moving down the gum between teeth. Occasionally, gum bleeds due to food or lodging between teeth obstructed the flow of crevicular fluid. Flossing induces bleeding which improves drainage.
Maybe. You could be cutting yourself with aggressive flossing, but this isn't likely or else you would know it. It's really easy for the dentist to take a few measurements and x-rays and see what is really going on.
Yes. Healthy gums do not bleed anymore than rubbing your hands together should cause bleeding. Bleeding means there are small ulcers in the gum tissue that are caused by bacteria. Consider using something like the perio protect method that uses special trays to deliver hydrogen peroxide gel into the infected area. This kills the harmful bacteria and you can keep them from coming back with regular use.