How long do I need to be freelancing before applying for a visa in Thailand?

Read the website of the Embassy to apply at.

Depends from which country you apply. Simple as that

Most of what you're asking is Embassy specific, 3 months is generally enough, if you can show you have a portfolio and client list and appear genuine. A lot of it is having a brief convincing cover letter. As far as bank statements there are 2 different types, the 500k funding, and the freelance income payslips/deposits/ whatever related to your contracts/gigs. On top of that a tax return might be requested, in your case of only being viable 3 months it's moot. Again, it's up to you to provide a convincing application with a brief cover letter explaining how your situation and documents either tick off the boxs, or the reason why it doesn't.

I think that you've seen conflicting information because not everyone is asked for the same documents. It depends a lot on the embassy where you apply so check that website and see what documents they want from you.

I think there is no requirement to run your company for any number of years so in theory you should be fine if you meet all other requirements, especially the business proof and financial proof.

But again it is up to the embassy, they can request more docs than what is originally listed on their site.

Where are you applying? Answers are embassy specific. There are DTVers with 1-3 months as freelancers. Tailor your application to the specific embassy you will apply from.

The answer is it depends on the embassy and the day 😅 Requirements are constantly changing and vary.