Vintage Dances and Bands
The band is the key to your vintage dance event. Recorded music, no matter how good, will always make your event feel, somehow, incomplete.
It is fine for dance classes, informal get togethers, parties and intervals between band sets, but I for one have never been able to bring myself to charge people actual money to come and dance to recordings.
The first consideration with a band is their suitability to the theme. There are a lot of what I call "wedding bands" out there, who haul around a lot of extraneous electronic luggage and have a dull, generic sound. I find this to be the case with most bands playing "modern standards".
Nearly all of these bands will tell you they can do "vintage" sounds like 1920s jazz, or ragtime, or Victorian--but do not take them at their word. At the very least, get a demo recording and if at all possible, try to hear them live doing the thing you want them to do.
Another issue with proper "fit" is on the other end of the historical spectrum. Many dance bands that play for contra dances, English country dance and the like have a modern sound as well, or perhaps a sound that is too American folksy for an event that is not set in the Old West.
The key to selecting the band is deciding what you want the spirit of the event to be, and finding the band that can do it. You should, of course, be realistic, and not set an impossible bar.
Another big issue with bands for dances is their ability and willingness to play for dancers. Many (most?) musicians have an esthetic sense that is built around the sound and emotional impact of the music. They think about tempo as a tool for self expression and not as the absolute foundation of a dancer's experience. For this reason, they will play fast to be "lively" and slow to be "soulful" even if their tempi are too fast or too slow for comfortable dancing.
Worst of all, they will arbitrarily change tempi, not to add variety and challenge for the dancers, but to give that emotional musical "punch".
Many otherwise capable musicians need to be patiently and respectfully trained to play for dancers, and then frequently reminded (again with patience and respect) when they stray. This is a job that often falls to your MC or dance master.
Another frequent issue is variety. Many musicians are comfortable with certain types of music, and like to stick to those genres, even when they make for dull dance programs.
1920s-40s dances may well fall into Fast (two step/balboa/swing) and Slow (foxtrot) programs, that can get a bit dull. They can greatly benefit from the addition of tangos, rumbas, waltzes and the like. It doesn't help that many of the American bands of the period didn't really have a particularly varied program, so modern bands with a limited variety are not being unauthentic. However, if you have a ballroom dance crowd, one would do better to follow the lead of the European bands of the Jazz/Swing era, which did have a more interesting mix.
At this point, I should mention that I am not a swing dancer, even though many of the programs I do overlap in terms of period. I know that the today's swing community has certain expectations, and one should always be aware of one's audience. So, if you are a swing person, you can tune me out, though I might respectfully suggest that variety is still the spice of life, and there is more to life than the Lindy.
On the older dance front, there are many events that can't seem to get out of the Waltz/Polka/Waltz/Polka rut. I have already addressed this in an earlier post, but I will again repeat that variety is a good thing.