Look I'm American who has been living in SE Asia (mostly Malaysia) for the past 10 years. I've spent lots of time and worked in lots of countries here including Vietnam, Thailand, Philipines, Singapore, India and obviously Malaysia.
In Asia a work visa is intended for foreigners working for locally incorporated companies. Regardless of what it says on the websites, if you have a tourist visa you are free to startup / bootstrap your new enterprise. If your coding up a new website, hosting it on Amazon and serving customers over the internet your not really doing business and the country your living and honestly no body cares. It's cool.
If you want to start selling to locals, offering consultancy services to locals then yes you should probably get a visa. But of course you don't need the visa until you are actually doing that.
People who quote websites stating "facts" about visa's in SE Asia obviously don't know how the law works in SE Asia. In SE Asia the law is a guideline and your clout / how you treat people is much more important than the words written on the page, when it comes to the courts and the interpretation of the law.
So if you want to bootstrap in Asia, chillax and just do it. If your too worried about it, your probably won't adjust well anyways.