Do I need a separate business bank account or can I just use my personal one?

You are not legally required to have a separate account as a sole proprietor, but you should, and if you formed an LLC or corporation it is close to mandatory in practice. Mixing personal and business money can let a court 'pierce the veil' and strip away your LLC's liability protection. Even for sole proprietors, a dedicated account makes bookkeeping, tax deductions, and audit defense far cleaner because business transactions are already sorted. It also looks more professional to clients and is needed to accept payments in the business name. Open a business checking account, route all business income and expenses through it, and pay yourself by transfer to your personal account rather than spending business funds directly.