What are my options for extending my stay in Thailand as a 67-year-old retiree with a NON-O visa?

I’m an Irish male 67, with a non immigration O single entry (with “retired” remark) eVisa obtained from Thai London embassy (they also issue for citizens of the Republic of Ireland in recent years). Background; I have a long term Thai gf (>18 years together.. we are not married. I stay at her house in Korat).

A couple of questions relating to an upcoming trip in Nov:

1. Can I extend this visa at an internal immigration centre or do a border run with ease and return for 30 days as a tourist (no visa needed?) just prior to the evisa expiring?

2. Following that extension or return in Point 1, I need to go to Australia for a few weeks.

3. What are my options to return to Thailand again for another ca. 55-60 days before returning home to Ireland next April/May? E.g. Apply for another 90 days eVisa whilst in Australia (as if I was applying online from Ireland) OR enter again as a tourist (no visa needed?) for 30 days and extend it internally for another 30 days.

I guess I’m wondering are there any limits to the number of tourist entries and / or extensions one can get per entry in a single calendar year that could trip me up?

I would effectively be seeking to stay ~90 days, then ~ 30 days, and then on return from Australia another ~60 days before finally returning home to Ireland.

Thanks in advance for your advice.