You can start by sending a simple form to HMRC (it's likely online nowadays), to let them know and they'll expect a self-assessment from you every year, its pretty simple to complete
You don't need an accountant unless you form a Ltd Co, and you don't really need that (though it takes away your personal liability should something go wrong)
You'll need liability insurance for sure, but that's also straightforward
Better to open a new bank account IMO, keeps things separate. Plenty of free personal accounts and free business accounts for sole traders if you want the business name on the account