Homes follow the code and the codes take into account average/normal loading. It is possible to overload/overwhelm any house circuit also and the panel will not allow that.I’m a little confused by all this. When they build a house, the electricians don’t know what the potential load will be but they wire it anyway. Isn’t there a rule of thumb, like 5amps per outlet or something like that? I don’t know how big his band is but my band practiced in a room that only had 2 X 15a circuits in it and never tripped a breaker.
This project is a little different as he is asking for something quite a bit larger than any typical extension of a home system and at first an unknown need for so much power. Now we know a little more but powering a band can be a wide range of requirements. Your band needed less than 30amps and that is what I would also expect for a little local band. Then on the other hand I’m involved with the building of home theaters on another forum and there are quite a few people that have such massive home theaters they also have 8-10 20amp circuits. It seems crazy to me that it takes that kind of power to watch a movie at home but banks of giant speakers with huge amplifiers can really suck up power.
I have a 100amp sub panel run to my garage shop and barely ever draw over 30amp the wire running to it has to be sized for the possibility of full usage. Then you also have to factor in the type of wire and the distance, along with what is feeding the house also.