@Ziggy ******
from memory you don't need the letter for the initial 90 day Non-O visa. But if you're applying for the visa inside Thailand you do need to have at least 15 days left on your current stamp when you apply as it has to go for approval (it's 21 days in some immigration offices, and I believe at least 1 office requires seasoned funds). So if you apply on the 15th you won't get the visa until the 1st of July and most immigration offices won't allow you to apply for an extension until you are down to the last 30 days, a few are 45 days, so no you won't get the 12 month extension by the 30th July