Personally, I’d only refer to HMRC advice & guideance on their website. Calling them takes ages and results in vague and imprecise advice. You’ve also got nothing on paper later when they contest it!
I believe that for 2 days/wk you’d be as well going Sole Trader.
There are Accountancy firms aimed specially at locums, usually working online. Friends on other health-care jobs have recommended them to me. They may be worth trying since they’re specialists in the field and the fees look amazingly low too.
Try googling ‘”locum accountant”. I have no specific recommendation. My experience is that accountants vary enormously in quality and expertise.