It is individual depending on age, situation and education.
If he has a pension from his home country, a monthly income of 40,000 Baht transferred to a Thai account for survival and income documentation for an annual extension of stay is sufficient.
No. You must have a non-o immigrant visa upon entry. The stay can be extended for one year at a time at immigration in Thailand for a fee of 1900 Baht, based on marriage to a Thai, or if you are 50 years old and meet the conditions.
Dirk C. Wendtorf is correct. But the official rules are that you can either document 400,000 Baht in a Thai account or 40,000 Baht in monthly income. Practice may be up to the officer in charge
I entered on a non-immigrant single entry. I got a multi-entry stamp in my passport for 3800 Baht at the local immigration office in Ubon Ratchathani. I could also get a reentry for 1900 Baht.
@Peter Hedley. To give a correct answer, I need to know your nationality and whether you are asking about visa on arrival or visa-free stay. There are 93 countries that have a 60-day visa-free stay.