For many events such as weddings, particularly larger ones, musical entertainment is a big consideration. For smaller events, you might want to consider playing music over speakers, perhaps with a mix tape or a compilation of suitable songs. For larger events you might want to hire a DJ, or even a band. Another thing to note is how you expect your audience to react to the live entertainment. Are they a more energetic audience that might want to dance, or the sort that might receive live music a bit more frostily? For the former, it might be a good idea to hire a marquee with a dancefloor or something similar for outdoor events. For the latter, it might be a better idea to hire a DJ to play music or just play your own music as mentioned earlier.
Live bands are likely to be the most expensive option, especially if it is a large event and you need very skilled musicians. It could cost over £2000 for the best bands, and ideally you want to pay more than £200 to each available musician, as this is the kind of pay that professionals expect. One of the good things about having your event in a marquee is the availability of good acoustics, as marquees are generally made of soft material that absorbs sound rather than reflects it, which means there are less echoes. Both live bands and DJs will need a power supply for their equipment, and sufficient space in which to play. It is generally accepted to provide band members with food and drink during the event.
Dealing with live music means you need to think about noise. If your event is in a residential area or there are people who may be bothered by loud noise, it may be best to talk to them before arranging your musical entertainment. Make sure to arrange some time for your band or DJ to set up at the start of the event, as this may take a significant amount of time. Finally, you should think about what genre of music you want for the event, depending on the crowd and the context of the event itself. What kind of atmosphere do you want to create?