Dumb flight/customs questions

You should not have to deal with customs at your layovers unless you decide you need to leave the airport's secured area.

There are no dumb questions. Ask away.

First, I am assuming this is all one one ticket, a through booking.
(If you have done this as two separate bookings you would need to collect your luggage and check in again for the second flight, in which case 1h40 is not enough time).

As far as you luggage is concerned, that is check through to your final destination (Naples). You do not see it at Paris. You need to go through customs at Naples, which involves walking through the green "Nothing to declare" after you have picked up your luggage. No problem.

Both France and Italy are in the Schengen Area, which means there are no passport controls on this flight, you will go through passport control in Paris, which is where you enter the Schengen Area. Should take less than 30 minutes with luck.

Flying back, Venice to Amsterdam is intra-Schengen, no passport checks. At Amsterdam you will have your passport checked for exiting the Schengen Area. You will not see your bags again until you reach the final destination.

Pretty sure you will have to go through PP control at CDG as this is your entry into the EU. Personal experience, me, flying to Graz through Munich, PP control in Munich only, bags transferred to Graz. Spouse and Grandson meeting me in Palermo coming through Brussels, PP control in Brussels, one of two bags making it to Palermo, the other catching up with us in Catania. As a caution, I would carry-on a couple of days worth of personal items when going through CDG with that kind of time between connections. It may be a "legal connection," however you are flying through CDG which I personally put at the bottom of the EU airports along with FCO in the EU.
As far as your return, bet it's AMS, your exit point from the EU,one of the top airports in the EU.

May the force be with You!

You did not say what city you were flying from in the US.

You will not see your bags again until you reach the final destination.

If your flight home is a direct flight from Amsterdam, that is true. But if you have another stop to reach home, you will need to go through US Passport control at your first landing in the U.S. You will also need to collect your luggage, then go through U.S. Customs, then put your luggage back on the belt so it can be loaded onto your connecting flight.

Thanks for the correction Sam. I just assumed the OP would be flying directly home.

JerryG, a small correction. "go through PP control at CDG as this is your entry into the EU" - the reason you go through passport control is not because you are entering the EU, it is because you are entering the Schengen Area.
The Schengen Area is a Passport Union, the EU is a Customs Union.

If, for example, you were travelling via London instead of Paris, the UK is non-Schengen, so you would stay airside at London, and go through passport control when you landed at Naples.

In the EU Schengen:
Going:
Passport control (immigration) at the first port of entry (Paris CDG)
Customs at the final destination (NAP) when you retrieve your luggage.

Coming back:
VCE to AMS is like a domestic flight. No passport control
AMS: Passport control before embarking to the US.
USA FIRST PORT OF ENTRY: Passport Control (immigration) and Customs.
Luggage is checked all the way from VCE to your final destination, however you need to retrieve it at your first US port of entry to clear customs. Unlike the EU, in the USA both immigration and customs is done at the first port of entry.