Collected from a lot of first conversations. Short answers, in the order they usually come up.
how long should the music run?
Sixty to ninety minutes for most gatherings. Forty-five in an office. Longer outdoors, where people drift in and out and the evening has a looser shape.
Under thirty minutes is a performance rather than a baithak. There is not enough time for a room to warm up, arrive somewhere and come back down.
do people have to sing?
No, and it helps if nobody is told they must. Participation happens on its own when the music is at the right volume and the room is seated close enough. Being urged to join in reliably has the opposite effect.
Expect perhaps a third of the room singing early on and most of it by the end, with a few who never do and enjoy themselves regardless.
what if nobody knows the bhajans?
It matters less than people fear. Congregational devotional music is built on call and response, so a line is sung and the room repeats it. You learn the melody as you go; no preparation is needed.
Familiar bhajans help the opening, so it is worth mentioning any your family particularly sings.
how much space do you need?
Roughly the footprint of a two-seater sofa for a small group, in a corner where everyone seated can see without turning. No stage, and generally better without one.
can it be outdoors?
Yes, with the caveat that open air swallows sound. A group that fills a living room will feel thin on a terrace, so outdoor evenings usually need a fuller sound and more contained seating.
what about children?
They are usually the best thing in the room. Clapping is the entry point, and children join long before adults do.
Practically: keep diyas at the edges rather than in walkways, and expect the front row to migrate steadily closer.
how far in advance should we plan?
For an ordinary weekend, two to three weeks is comfortable. Around Janmashtami, Navratri, Diwali and the wedding season, considerably more, because everyone wants the same evenings.
do we need to provide sound?
For a small indoor gathering, usually not. For a hall, a courtyard or a large crowd, yes, and it is worth sorting out who is providing what well before the day rather than on it.
what should we not do?
Schedule something in the middle. A speech, an announcement or prasad halfway through resets the evening rather than pausing it.
And do not leave the ceiling lights on.