How do you make a graph select the max and min for your Y axis instead of defaulting to limits?

[#1]

If you mean column property Spec Limits with "limits" then you could for example remove tick from Show as Graph Reference Lines if you don't want to see them at all.

Else you could use scripting after graph has been created by using Min and Max

or possibly Insert one expression into another using Eval Insert, Eval Expr, Parse, and Substitute to insert min/max values to graphs script directly (get script from graph and then modify it as needed)

[#2]

This worked! thank you, how can I choose the size of my data points on a graph?

[#3]

No idea if you want scripted solution or not (both are basically same as you can steal script JMP creates for you).

Right click on marker on legend and change the size

and if you need the script go to red triangle and get script from Save Script menu

Graph Builder(
	Size(548, 589),
	Variables(X(:weight), Y(:height)),
	Elements(Points(X, Y, Legend(3)), Smoother(X, Y, Legend(4))),
	SendToReport(
		Dispatch(
			{},
			"400",
			ScaleBox,
			{Legend Model(3, Properties(0, {Marker Size(6)}, Item ID("height", 1)))}
		)
	)
)