Should I book visas, immigration and long-stay planning in advance or arrange it locally?

Visa and entry conditions depend on nationality and purpose and can change. Use Thai government or immigration information and avoid treating social-media advice as legal authority. Advance booking is useful for airport arrivals, holidays and fixed schedules, while local arrangement can offer flexibility for ordinary days. Use an identifiable operator, retain written confirmation and understand cancellation terms. Very cheap unsolicited offers deserve extra checking. Immigration note: Entry and extension rules depend on nationality and purpose and can change. Check current Thai government or immigration requirements before relying on an older answer.