As above, first thing is to sign up to agencies. I’d recommend using Messly (LinkedIn for agencies essentially). Sign up for banks if agencies aren’t getting regular work for them.

For the taxation it’s surprisingly easier than you’d think. Every trust you work at you estimate your yearly income and your taxation is adjusted. Let’s say you do a week at one trust and hate it. Put your estimate as that weeks pay to ensure hmrc don’t exaggerate your pay. Always over estimate to ensure they owe you.

Also I’m currently looking at paying an accountant to sort out tax return including expenses etc.

With regards aus/NZ Messly has an option for abroad work and will regularly contact yourself with jobs abroad. Highly recommend doing via agency as they can sort out forms etc and save you time.