Depends on what you call a large amount. For 10k ($, £, €) etc then wise is probably the cheapest option. For 100k or above then your banks swift rate may well be the cheaper option.
What has that got to do with the price of cheese? What’s getting tougher? The need or not need to file a TM30? As stated it’s office specific. Nothing to do with Russians or Chinese.
That’s going to be specific to the immigration office you use. Some require a new TM30 if you stay a night away from your home. Some don’t care if you travel within Thailand and return home. Some don’t seem to care if you travel overseas and return home.
With no visa bought prior you’d get a 60 day visa exempt stamp on arrival and can extend that once for a further 30 days at a local immigration office. Leave and re-enter after that for a repeat of 60+30.