should I select departure airport based on number of flights to destination

For me, the trip cost trumps any other consideration (and preferably an airline that stops somewhere in Europe first, not in Philly or JFK or Newark)...and I don't plan based on worst case scenarios since they rarely pan out. I can't anticipate what alternatives an airline would give me if I was bumped (it depends on their codeshare partners and other variables), so I tend not to worry about it. I do pay attention to tight connections since your luggage may not get there when you do, but again, I've had that happen and it wasn't a huge deal...luggage arrived the same night or next AM. I would say let the airline worry about how to route you somewhere instead of you worrying about it...that's their job after you've paid for your ticket.

Based on my recent experience, I'd suggest Detroit. We flew US Air from Philadelphia to and from Paris, and I would never combine those 2 items (USAir/Philly) again. Because there was only 1 flight going to Paris, we took a regional flight to Phil. much earlier than we needed to to make sure of the connection, and waited about 5 hours in Phil, partly because the Paris flight was delayed due to a change of aircraft at the last minute. And on the way back we almost missed our connection because of a delay and a chaotic scene at the US Air international to domestic connection area.

Everyone has different pain thresholds. Money, the unexpected, etc. Mine is transfers and that doesn't seem to be a problem for you as you have direct flights to Paris. One thing I will note is that of all the air ports in all of Europe that I have had to change planes in Paris' Chucky-D was far and above the most miserable on all accounts. Now I will pay a few dollars more to avoid it. If I had to fly into Paris I would pick Delta/Air France without question, even if it cost 10% more. When going to Paris we fly into London, spend a couple of days (love London) and then take the train to Paris. I usually find better flights into Heathrow than I do Chucky-D as well. The two cities also combine to a really, really nice experience. For the London option American/British Air is my preference. Best of luck.

You have many ways to get to your destination, and you wouldn't make a bad decision on any of them. I generally try to avoid NYC airports, but the new Delta terminal at JFK is absolutely incredible. We came back from Italy through Philadelphia last year, and was very impressed with the terminal improvements. We had no problem at all. And Detroit does a great job on international flights.
At the other end, Amsterdam Schipol is a very preferred airport for me. I try to avoid Heathrow anytime I can, and I think their taxes are higher than other European airports.

If i am recalling correctly, the large exit tax at Heathrow does not apply to an ongoing connector flight on the same ticket inside of 24 hours.
AS for Philadelphia, I have seen (I am a local) numerous times where delays cascade pretty badly. If you are flying in the summer afternoon t-storms can be a major cause of this.We've sweated these out a couple times. I don't think US Air would put you on another flight from a different carrier.

The exit tax is built into the price of the ticket. You can't see it. It applies to all take-offs, regardless, and it includes landing fees, etc, as well - - they're just collected at one whump. And it applies to all British airports. If Philly to London is cheaper than Philly to Paris, it is - - there's no way the tax can up the visible/quoted price. An example of a place that has virtually no taxes or fees is Istanbul - - the airport is heavily governmentally subsidized in order to attract passengers; hence, US to Turkey is often cheaper than US to western Europe or the UK. They also sell fuel a heck of a lot cheaper, so the carriers don't have as much cost to recover per ticket. A similar situation exists with the Republic or Ireland - - there's not spit worth of difference in the gas to drift the extra few miles into Glasgow or Manchester, but the ticket price runs a couple hundred bucks or so less. False knowledge sucks. Thus endeth the lesson in airline operation economics. Say thank you. Amen.

I have to disagree on the Heathrow exit tax, based on this year's experience. My son flew roundtrip PHL to St. Petersburg via Heathrow on BA. The return flight required him to layover a day, as it arrived 5:30PM, too late to make their last Philly flight. If we had opted for the next morning (which we did not do because of the hassle factor for him and the fact that he had a friend in London he could stay with), the price would have been about $105 less than his staying another couple days. This was explained by BA that even with leaving the airport that night and returning 1st thing in the morning this was considered a direct through flight, and the additional tax a was not applied. When he opted for the extra days, this was now considered a separate flight with the exit tax. I went through a lot of permutations before we settled on his flights, and this always held. BA provides a concise breakdown of the various fees imposed, and you can see the exit fee appear for what was not a through flight.

Ruth, if this is your first time flying any lenght of time, you will find out really fast what you do or dont like about it about overseas flights. i, personlly, hate wasting and spending time in airports since i feel that time could be better spent being a tourist. this is MY preference and your mileage may vary. there are direct flights from PDX to AMS so im not to worried about it, but Delta did screw me last year on my flight to AMS. Not much you can do about it other than to enjoy the ride (sarcasm). what i did learn here was about the booking of flights as separate legs or as one flight so i take that to consideration when i book now. About all you can do is to book what suits your needs/wants and dislikes and hope for the best. on that flight last year where Delta screwed me, even my connecting flight was last. so the flying Gods werent with me that time. if you want to do the research to see where you have the most chances of getting over there, go for it. the east coast is more compact than out here, so you have more choices. on my recent trip, i stayed over night (o/n) in AMS just in case of any issues. Its a waste of a day(s), but im in experimentation mode so i may not do the o/n stay next year. it will depend on how long of the layover on my connecting flights and if i want to spend another 6 hours on a plane after getting off a 10 hour flight. happy trails.

Airports to choose from? What a good problem to have but one not familiar in this area.