Supreme Court justices should have single term limits of twenty years, allowing every President to select at least one for the court per term.
However, each President should only get to pick one justice per term (two Justices for two terms if reelected). If more than one vacancy is created during a President’s term, then the longest serving federal judge should fill the vacancy and gain the same twenty year term other Justices on the court have. If two or move federal judges have the same longest serving time in the United States, then the Senate should decide who gets to fill the vacancy similar to when the President nominates someone to the Supreme Court.
The President should have no say in who the federal judge who replaces a vacancy on the Supreme Court should be if they have already replaced a previous vacancy within their term.
State officials preferably should be the same, but I believe its better that states decide that for themselves.