Geneva is a nice destination, and very GA friendly.
Your likely general flight routing will be towards Reims, then down to Dijon, before heading into Geneva, probably around the corner by Bourg.
If you need a comfort break, a better bet than Amiens/Dijon would be Reims Prunay. Customs is available here by PPR and there is decent restaurant on the field.
Amiens is deserted much of the time, and somewhat of track.
As an aside, it is not clear from your posting why you feel the need for a dedicated customs stop anyway. You will have to clear customs going into Switzerland in any case (The GA Side of Geneva is technically in France, but your passport will be looked at by Swiss Customs too).
In any event, make sure that you file a flight plan for your VFR (I assume) leg into Geneva. Ad hoc VFR flights are regularly denied permission to enter the Geneva TMA if traffic conditions are busy. Check the weather too. Geneva applies strict VFR minima to visiting aircraft.
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