Need help planning first trip to Paris please.

All the trains from Paris to Amsterdam go through Brussels. I'd recommend taking a morning train to Brussels, heading into the town center (easy metro ride) having some moules frites and walking around and then hopping on an afternoon train to Amsterdam. Each train segment is about 1.5 hours.

For your general questions - what neighborhoods to stay in, a nice hotel - of course get a good guidebook or two. You'll need it to carry around on your trip, it will likely answer your specific questions as well or better than anyone will here, and it will also answer a lot of questions your wouldn't think to ask. For your specific question, there's plenty to keep you busy in Paris for months, much less a week. Whether to split up the time depends on how often you expect to come back to Europe. If you expect to only have a few trips in your lifetime, get a taste of some other cities. If you expect to make it back periodically, I'd focus each trip on a smaller area. In either case, do a side trip to another part of France; the train system is fast and efficient.

If you're not sure when (or if) you will be headed back to Europe, hopping the train to Amsterdam once you're done in Paris would be a great study in contrasts: Paris is enormous and glitzy, Amsterdam is small and approachable; Paris is justifiably precious about its food, art, and history, while Amsterdam is much more laid-back and unpretentious, etc. The train from Gare du Nord to Amsterdam takes about 3.5 hours, and once you're in Amsterdam you can walk most everywhere.

You could crib from Rick Steves' http://tours.ricksteves.com/tours/paris. Paris definitely can keep you busy for months. If you really want to split the trip, then Amsterdam is a classic study in contrasts.

And since arco beat me to it by about ten seconds, I'll pick up the other bit. Where would be the "SOHO" of Paris? The Marais is the obvious answer, though I'm fond of the 5e around Rue Monge, near the Mosque: it's a properly lived-in part of central Paris.

Yup, nthing the Marais. Lots of great little places to stay, and you can get a fairly cheap room if you're willing to forgo some luxuries. If you leave Paris you risk spending a fair portion of your week in transit. And there's lots to see in Paris!

I highly recommend moving out of your expensive hotel and into someplace cheaper (easily had in Paris), and spending the savings on food. Meals and walking around, this is what you'll want to remember from your trip. And the new divide in Paris is not Right Bank/Left Bank, it's east/west. The neighborhoods in the east, including the 5th and the Marais, but also Belleville and the Canal St. Martin area, among others, are more Village/Soho-like than the neighborhoods in the west.

I would ask your question on the Slowtrav.com France forum. There are some incredible people on that board who live in Paris who can direct you to the right neighborhood, hotel, restaurants in the area of your business hotel as well as in the next neighborhood you stay in. Agree that the Marais and the 5th and 6th are the Sohos of Paris. 5th & 6th have the Jardins Luxembourg, the Central Park of Paris, so that's something to think about. I know it'll be November, but it's always a beautiful oasis to pass through while you're en route to many sites. You might also enjoy a quick lunch near the Canal St. Martin, which is kind of the Williamsburg of Paris. Keep in mind that getting to and from Amsterdam and Barcelona will eat up the greater part of both traveling days unless you can depart for home from the second city. If it were me, and I wish it were, I'd stay put in Paris but take a day trip or two out of Paris--Chartes, Chantilly, Senlis. Slow Trav has a whole listing of great day trips out of Paris in their FAQ. Have a wonderful time.

You could easily spend the entire time in Paris without running out of things to do or meals to eat. If you decide to leave Paris, I would not go as far as Barcelona or Amsterdam, but rather stay within France. Paris is the New York City of France: Paris is Paris, it is nothing like the rest of France. Within a couple hours journey, within France, and totally different from Paris, I would recommend a 1-night 2-day visit to Rennes, St Malo, Mont St Michel, Lyon, Strasbourg, Etretat, Honfleur/Normandy beaches. These are all easily arranged by train and within 2 hours of Paris: tickets bought online, hotels reserved online, except the last two, which are more rental-car friendly. If you really have to get out of France, there is no better place to go for stereotypically romantic cities than Bruges, Belgium. Those recommending the Marais have the right idea.