Immigration rarely asks for it at all, but if asked you must show 20,000 baht in cash or the equivalent in foreign currency, not your bank account, credit cards etc, must be cash. But 99% of the time it is not even asked for.
So easy to do your visa yourself if you are organized and meet all the financial requirements it’s not hard at all, no need to pay an agent to do it for you.
No unfortunately not, most offices will let you do your next extension with 30 days left on your current extension, but if you are not going to be in the country, your extension will run out and you will need to start the process again.
Yes, but be aware if you are spending 3 months consecutive in some countries, their law requires you to get a license for that country, it just doesn’t give you the right to drive for 3 years in another country.