4 hours should be plenty for Schiphol (AMS) in normal circumstances.

When you check in for your first flight, see if they will check and tag your baggage all the way through to Italy. If they have an “interline” agreement with Transavia, then your first airline should be able to do this—you’ll just have to present your Transavia e-ticket print out and itinerary to them (again, if they interline with Transavia). If they do, then you won’t have to fetch bags and clear customs until arrival in Italy.

However, if first airline can NOT check your bags all the way through, then of course you’ll have to fetch it, clear customs, exit to arrivals hall, then check in with Transavia, go through security, etc. No big deal, and again, 4 hours should be plenty of time. Use the luggage carts—they’re free at AMS.

I’ve gone via AMS a few times on separate tickets, and with long layovers. I always like to stop at the grocery store in the arrivals hall, get some juice and croissant, then go outside for some air (and sun, if lucky).

4 hours should be enough time to get baggage and clear customs if everything goes right.  Schipol is pretty well set up and runs pretty efficiently, but it’s a huge and very busy airport.  Just remember there are lots of other things that can cause problems even if your flight isn’t late.  There may be a security shutdown, other flights might be late so they’re handling twice as many people and bags as they’re staffed for at a given time, etc.  I was once on a flight from Atlanta to Paris that was 3 hours late because thunder storms in NYC re-routed so many other transatlantic flights — it was perfectly clear in Atlanta.

Whether or not I’d risk it depends on the consequences:  How much money are you out if you miss the connection — both the ticket you’ll waste and the cost of the a last minute ticket?  Are you likely to be able to get on another flight the same day or could you end up losing a day?  What happens to your plans if you don’t get to Italy for another day?

Thanks for the quick reply!  Basically, if we lose out on the flight to Italy, we’ll have to wait until the next day to leave (at least on Transavia).  We would lose the time we wanted to spend in Cinque Terre (we were flying in to Pisa and then spending a day and half there) and we would just basically go straight to Florence.  Now that’s assuming that something goes wrong.  I’m going to have to take my chances however, because this was the best way to do my itinerary after weeks of research.  Hey Don, what was your shortest layover in AMS?  And did you check your luggage each time?  Thanks for the tip on the baggage.  I’ll find out if we could do that.
 
Thanks again!

From my experience, Schiphol was one of the easiet airports to navigate, anywhere.  It took no time to clear customs and my bag was there almost immediatly.  I remember flying in around noon.  If you have 4 hours, you should have no problem whatsoever.

I’ve had same-ticket connections at AMS with less than 1 hour, no problem, but of course it’s all together with NW and KLM usually when I was through there. I’m so comfortable with that airport, that on separate tickets (situation like yours) I personally would cut it as close as 2-2.5 hours, but only because I’ve been through there so much, and know my way around fairly well. Four hours is better, of course. And a lot can happen to delay you—aircraft problem after boarded (happened to me at ATL to CPH; 3 hour delay after boarded due to mechanical problem), weather problems ahead of your route, fog, strikes by security, airline personnel, baggage handlers, power outage, computer problems, baggage delays… a lot can happen, but 4 hours covers you probably 99% of the time. I agree with oldlady though—if you have a lot invested in getting there on time, then see if you can work around that. For example, maybe see if you could standby for an earlier (nonstop) flight to AMS with your airline, or travel carry-on only (probably won’t work in this situation). But if the savings was significant using 2 tickets via AMS, then the risk might well be worth the potential gain.