Well, tbh, from my hearings of friends around me, I would say that the culture of firm or even team would likely affect your experience in any firm, Big 4 especially, with the fact that you actually okay with nature of audit work.

Then in terms of joining commercial or not, I think you could take more time to think through what you want to achieve, as there are lot of choices out there with joining commercial - AR/AP, finance related etc. Other services within Big 4 - Tax (Corp, Ind or TP), Risk advisory (internal audit similarly), Accounting services (accounting standard advises), Financial Advisory (M&A, Valuation, ICP, Econ); or other professional services firms. I would say there are actually many choices out there, do not limit your paths especially when you’re still fresh and thinking where’s next to head, try explore more to have better picture.

In terms of time for study, there are some companies actually provide study leave for you to pursue professional qualifications, so you could just check with HR / during interview and it could be one of your consideration factors in selecting companies.