You will get a extension till may if your passport is valid till may. If thats what you want you not need to do anything. But if a extension till september, for a full year is better then renew your passport early before september. Think about proof of funds issues...
You can come on visa exempt thats 60 days visa free entry. In country you can still extend that for another 30 days. So you can come for 90 days without a visa.
You can not start with monthly transfers at your first extension. Thai immigration tend to ask proof of 1 year monthy treansfers with a minimum of 65k baht.
You can request a 7 days extension at a local immigration office, do a border bounce or better you get a 60 days tourist visa before you go to Thailand.
The only visa available at the airport is a Visa on Arrival. Thats a 15 day visa for citizen of about 30 countries. That visa needs to be requested and it cost 2000 baht.
Most tourist though can enter visa free. NO visa. Its called visa exempt.
I didn't know anyone and got a non o visa. Many do this every day. So whats the issue? Do you want us to read between the lines and guess your real intentions?