Getting a Non-O sorted before you come on your first trip will enable you to get your bank account sorted early so you don't have to rush it at the start of your retirement.
And getting a Non-O on your first visit lets you avoid going to Immigration during this visit. 🙂
Just travel around, find your pace, enjoy your life, no extensions needed.
And then in 6 months come back armed with a Thai bank account seasoned with the required amount of money for the upcoming yearly extensions, without having to stress to arrange it all out on arrival.