There are prescription-only high-fluoride toothpastes. Excessive fluoride (more than you can get from Act + normal fluoride toothpaste) can cause fluorosis, which ends up being bad for the teeth. Normal amounts of fluoride are good for the teeth. The prescription-only toothpastes have enough that you don't want to use them regularly for a long period. As with most things, the dose makes the poison. Some dentists prescribe them even when they're not needed, since it won't be harmful to use a tube of the stuff every year, or even every 6 months, and it's profitable to them.
I thought it was floss -> mouthwash -> brush, but either way brush was always last because the toothpaste fluoride is what you wanted left on your teeth at the end of the process with the mouthwash serving as a base layer.
I think the most important thing is to make sure your process leaves a fluoridated product in your mouth at the end. You want the fluoride to stay on your teeth for 30 minutes.