There's no "FIS" along that route - if you call Paris Information you'll just get a lecture on how they have no radar. However, you do need to be in radio contact most of the way, because much of that airspace is Class D. No problem - the folks along there have always been extremely friendly, in my experience.
At mid-channel, talk to Lille Approach (who will give you a squawk until you leave their area, but probably say nowt else).
If you track ABB direct PON, then talk to Beauvais on 119.9 - they will normally clear you through their TMA and possibly also CTR - it's all Class D so you MUST talk to them.
They will either hand you over to, or suggest you call Pontoise on 118.8, and again you MUST talk to them as it's Class D.
From Pontoise, you may be given someone else to talk to (I once got sent to Orly who are theoretically the "Approach Control" for Toussus but may not want to know). Otherwise, go to Toussus.
Heights - yes, it's critical! Look carefully at the half-mill, or get the special "Paris Region" chart. There's a good one in Bottlang. Airspace is "variable" depending on whether or not Creil and Bretigny are active, etc. Creil won't bother you, but Bretigny might, weekdays. I've never known them open at weekends, but anything's possible.
Basically, you need to be above 2000 feet AGL to cross R53D between ABB and PON, then below 3500 feet before the Paris TMA - which is before you get to abeam Beauvais.
After that, it's regular descents - above 1500, below 2500 for the Pontoise TMA transit, then below 1500 from there to RBT to TSU. Somewhere along there, Orly/Toussus will give you QFE and want you at 800 feet QFE.
You absolutely must have the VFR "plate" for Toussus, because of the "avoid" areas - but it's not a problem with the plate if you keep your eyes skinned. If I can do it, anyone can.
Leaving is easy - to 1500 feet QNH and to Dampierre, then to 2000 QNH and direct to Pontoise.
It's a great trip, and if vis is OK the pax get an excellent view of Paris. You won't see as much of the view, because you'll need to have your eyes very much out of the cockpit looking in front of you for traffic: that airspace can be extremely busy. If you can't see three aircraft in front of you going your way, and two coming the other way, you probably aren't looking hard enough. In theory, ATC will tell you they are there, but in my experience they often don't.