Jeff Georgantes shows the Miland Synclastic & Anitclastic Pliers 

Hand strength is a very personal thing, so I can't answer for all, but I can say that a person with average hand strength should be able to use these pliers. For your thickness question, I'm not sure if there is a recommended maximum thickness by the manufacturer? That said, these pliers are really sturdy and very well made. You'd have to experiment to determine what works for you or not. Also, don't forget that one of the most important traits of anticlastic and synclastic metal forming is being able to create forms with volume (size) and not a lot of mass (weight). The techniques are generally rooted in thinner gauges, like 20-24 ga. (maybe even 26 ga, if you're careful!). Those compound curves create volume, without excessive mass. Hope that helps! Jeff

Thanks! @@jeffgeorgantes48