I believe that people generally need lighter tripods/tripod heads than they think they need.
That said, I think that the answers to your questions depend on your style of photography. Are you going to be using a 2-lb. Toho monorail or a 14-lb. Toyo? Will you use the tripod in a studio, in a desert, or both? Do you need it to be extremely precise? Will you be lugging it on 30-mile treks in the Rockies? So much of this descision is based on your personal preferences.
I use a Manfrotto tripod/tripod head combination that is relatively light (about 6lbs.), but it's heavier than I need it to be for my 4-lb. Tachihara field camera. I've also tested this combination with a 10-lb. monorail made by Linhof. The tripod was a little light for that camera, but would have been okay for many uses.
I'd suggest that you test your current tripod with the camera you'll be using. You may not need the pain of paying a lot of money for a lot of weight.