A. BOSTON! or a suburb thereof. Spring can be lovely in New England... "Boston, cradle of liberty, home of the Bean and the Cod, where the Cabots speak only to the Lodges, and the Lodges speak only to God." Not far from Salem (witch trials), Plymouth (Plimoth Plantation, the Rock, and the Mayflower), setting for The Scarlet Letter (well, nearby). The Boston hotels can be pricey, but there are alternatives in nearby suburbs.
Easily reached by air, road, or AMTRAK. And South Station is right downtown, too, in Boston. Boston has a great public transit system, and is truly a "walking" city.
You could even try Worcester, MA, although I'm not as familiar with it. Or, Hartford, CT is also a good city with lots of hotel rooms.
Convention bureaus to help you out... http://www.bostonmagazine.com/
B. You can find lots of people from all over the world here. The city is very safe, in fact, it's in the top 10 list of the safest cities in the US.
For those seafood lovers out there, Boston is the perfect place to visit. There are many restaurants all over the city and they're great.
The weather around the end of April to mid-May is very nice. The leaves on the trees start growing back, and everything is green. The foliage is simply beautiful.
If you're a big shopper, Boston is the right place to be in. There are stores everywhere. Take a stroll down Newbury Street, where you can find shops of all kinds. From vintage stores to exclusive ones such as Giorgio Armani and Burberry's.
Boston is great for the whole family. There are such places as the Museum of Science, the Museum of Fine Arts, and the New England Aquarium. From Boston, you can go to Salem and visit the Witch Museum.
In short, Boston is one the greatest cities in the world. Coming from a person who's not originally from Boston, or anywhere in the United States, that's indeed something.