If you’re selling B2B services, anything you sell to a client based outside UK is outside the scope of UK VAT, so that simplifies that issue. I would imagine the extra headache of routing funds through multiple entities is unlikely to be worth it, unless clients in the USA/Australia are making you jump through hoops, repeatedly, to prove your tax status?
We have (and have had) a few digital marketing clients. One was a total nomad and relocated their business to the states as most of the higher paying clients they had were based there, the rest simply bill from their UK limited company without much issue, and they have just as many high-paying clients 🤷♂️.
Anything you’re specifically looking to minimise/maximise about your setup?
Check out https://www.gov.uk/set-up-sole-trader - the guidance there isn’t too bad. We’ve not helped anyone under 17 navigate this before though, so I’m unsure whether you’ll face any hiccups along the way. I can’t imagine HMRC will turn down your tax contributions from self-assessment though 😉
Anyway, there’s nothing to do until you’ve brought in over £1000 revenue (that’s revenue, not profit) in a given tax year, though. Then you’ve got until October 5th the following year to register (unless they move the goalposts in the meantime) 👍
But it often simplifies things to register as self-employed sooner, in case anyone needs to see evidence of it - like opening business accounts, for example (there’s no requirement to do that, but it’s worth keeping your business transactions separate, even if it’s a different personal account you use).