LFPN has customs throughout its opening hours, I believe. I don't always bother speaking to Lille. Beauvais and Pontoise are both helpful on the way down. Caen are useful if coming in from the West (with a radar service, but are only open during the week).
Get the Toussus ATIS ASAP before your arrival.
Have fun, and I hope the CB's are fewer than are promised over mainland UK for tomorrow!
Final tip: be sure to get the fast RER into town from Versailles, there are several that stop at loads of stations.
PPPS: there is an excellent pilot shop in the tower, where you can buy French maps more cheaply than Transair (not difficult).
[This message has been edited by skua (edited 25 August 2000).]