I've never used it but my guess is that the Wi-Fi won't be very reliable on the train. I'm just thinking about how many people would be sharing that signal. Check out DTAC because they do similar offers if you have a phone then just go to somewhere like 7-Eleven and they can top up your sim card with a data package
These are the steps I took. I came in on a 30 day exemption and then applied for a non-O. I then seeded the 800k for 2 months and then converted the visa into a one year stay based on the retirement.
if you're staying here long term you have to go to the immigration office every year anyway to renew the retirement extension. And then there are 90-day reports. Last time I renewed my extension it took about 20 minutes. So whatever way you do it you can't avoid the immigration office.