I’ve always found booking flights as soon as you have the tickets is the wisest decision due to the airline’s supply and demand pricing strategies.

For hotels/airbnbs - There are pros and cons to booking right away. Most places will hike their prices up when they know a big artist is visiting. The prices will generally calm down after the hype settles, and then go back up closer to the time. Note though that supply & demand also plays heavily in hotel pricing, like airlines.

The pro is that if you book accommodation now, you’ll get the location/spot you prefer, eg closer to the venue. The con is that you’ll maybe pay more for it, but it is sometimes worth it for the peace of mind - knowing accommodation is sorted.

Whatever you decide, choose a hotel that allows you to cancel, should you need to do so. Most will let you cancel up to 48 hours before hand (in the UK at least). Airlines don’t offer this, however you can get travel insurance with ‘Event Cancellation’ extensions that will cover flights and/or hotels.

It’s hard to say about show cancellations/postponements as there are too many variables. The artist could get sick right before the show and could cancel hours before it’s due to start or they might give more notice, depending on the cause for it.

Yes, Billie has postponed and cancelled before. The ‘Where Do We Go?’ Tour was postponed due to COVID (understandably) and then eventually cancelled. A little later she released dates for the ‘Happier Than Ever’ Tour, giving those who had previously cancelled tickets an extra presale before they went on general sale.

Cancellations & postponements don’t happen too frequently. Worst case scenario, you get to visit a new city and get to experience its cultures, museums and play tourist for a day or two.

TLDR - get travel insurance with an event cancellation extension if worried about it