I've used the 400k for the past two years and I bring over more than 40k a month using wise for living cost and my sons education. I'll still have the 400k this time around but will also bring evidence of monthly transfers over the 40k and see what immigration say
Look at Ajarn.com website. A lot of schools in Thailand post job opportunities here. You can also post your cv so schools can also check your qualifications and suitability for them. Best to try to get a bilingual school or a school with an English progmme rather than a Thai school as salaries are usually higher.
If going from uk to the republic of Ireland a uk visa is all needed. If going the other way two visas are needed. Ireland is not a member of schengan so other countries will need that visa also.