If you are not getting flow from the rad to the overflow, then check your cap. might consider replacing since it's only 14 years old. Pull the small hose that goes from the rad to the overflow and try blowing through it. That is all I can figure for you on the issue of overflow. If it's not circulating, then there's a chance that you are building too much pressure and the coolant is being forced somewhere else that it isn't supposed to go.
Seized plugs - not too normal, but I know two of them are PITA's. The color of your plugs are ok - grey/white and chalky kinda...normal colors. Black sooty or greenish tint are bad.