I play in the US version of the OP's sort of group - an open contra dance band. We mostly play unamplified, with the caller having her own mic system. If we lack a piano in tune, we bring an electric keyboard, as piano sets the pulse and pace of the band. We typically have 12-36 players - hammer dulcimers, fiddles, recorder, banjo, mandolin, upright bass, single autoharp & concertina. Only 4-10 will show up at a rehearsal, though.

We use our sound system when we play dances in spaces with horrid acoustics - like a gymnasium - or for family dances with streams of screaming wee girlies. Piano has it's own amp. We use about 8 mics, placed between members, who sit closer than usual. The melody players get more attention, particularly if they're outnumbered by rhythm players - then our stronger hammer dulcimer players may get a mic of their own. We get to the amplified gigs an hour ahead for setup and sound check. Those who don't bother to get there early may not be near a mic at all - part of the risk of an open band - not everyone has the same level of dedication. (wish we could dole out the pay with the same negligent attitude)

What having the sound system requires, outside the considerable cost, is having someone who knows how to set up and run it available for all gigs,& someone to store and transport the system. All of those are big commitments. The advantage is being able to play a wider range of gigs. YMMV.

Joanne in Cleveland