Bruce i apologies for tramping your thread but things like this puts doubt in new comers minds and they then abandon their projects because it gets too expensive. Advice on your Z though is definitely not go for 1610 screw enless you are using high powered steppers. The greater the thread angle the easier it is for the stepper to not be able take the weight. Please do not ignore Jonathan's advice as he has a lot of experience learned first hand. Just stick to your budget and if it is not enough for what you really need then save rather than waste it on buying the first thing that comes along.

A great effort on your build so far