The distinction between Federal and state judges isn’t terribly relevant. There have been SCOTUS justices before without any Federal experience. Heck, without any judicial experience at all.
Experience as a state judge is actually completely relevant as you’re required to interpret the intersect between state and Federal law, something SCOTUS has to address regularly in many cases.
State judges CANNOT hear or rule on cases that fall under the exclusivity of federal jurisdiction.
Yes, there have been justices who had little or no judicial experience (Elena Kagan is one); but the lack of such experience gives a senate fence-sitter an excuse to reject a nominee. That was my point.