I disagree - I have gotten evisa while in Thialand. Without any issues at immigration. I think the difference between what you are saying and what I am saying is experience. You are regurgitating what you've read and I am speaking from experience :)
You can apply for a visa online. I have never had a ED visa but I have had a few questionable visas. I have been pulled aside at immigration a couple of times and each time, they said "when you come bacK...", not "don't come back" nor have I been denied entry.
You take a risk, so consider having a plan B. I would recommend crossing at a land border at least for the first time. This way if they deny you entry, you can walk back to where you came and try a different land border. Have a good story, you met a nice Thai lady and you're thinking about getting married, or something. Whatever the story, you will want to be able to provide proof.. Hence, if you go the girlfriend route, have a Thai lady friend available for the immigration office to call (it probably won't come to this but it's better to be safe).
Another thought, get a visa online, go talk to an agent about doing a border bounce (because you already have the visa you only need exit and come back). Agents often know which borders are easiest to cross and which immigration officers are friendly.
The Thai Embassy, US, asked me to provide documentation for the minor I was travelling with, which is very strange because I wasn't travelling with a minor. I wrote a note/letter explaining that I was travelling alone, with no minor, and I would not be able to provide documentation. I converted the letter into a PDF, then jpg, uploaded it and they seem to accept it because the gave me the visa.
Additionally, I used my condo instead of a hotel booking, they requested this same paperwork a couple of times. Condo paperwork is all in Thai and I didn't understand that my name was not on the front of the paperwork, so I uploaded the paperwork, they found it inadequate and re-requested. They requested 3 times. Hence, you may want to try the letter explaining your plans... They may accept it or reject it and re-request your onward travel documents.
I just got an METV (Multiple Entry Tourist Visa). I applied online. I was not in my home country when I applied. I am US citizen and I used the Thai Embassy from my home country. Maybe the Thai Embassy in the UK is as flexible. I did have to get a little creative with the paperwork but its worked out for me several times. Good Luck
If it comes to it, Bali will be my secondary location.. 90 days x 2, I will find some place to go for a couple of weeks. 90 days TH, 90 days ID, 90 days TH, 90 days ID, some place for a week or two.
I am skeptical the taxation will become a thing. With double taxation treaties in-place, and new or newly enforced taxation just means more paperwork, not necessary more taxes but who want more paperwork either.
I have been working online/remotely for a few years now, mostly on tourist visas. There *may* be tax concerns in the future but mostly if you are not taking a job from a Thai person, there are little concerns about working online.
Its a common question. The fastest easiest options are find a bank that will sell you an "insurance policy" to open a bank account or find an agent to open the bank account for you.
You might be able to apply for the visa in your home country, come in on that visa, go to immigration, get the letter then go to the bank. That might, legally work, but I am pretty sure most people exercise one of the two above options. FWIW, I bought the insurance policy.
I bank with Bangkok Bank and haven't had any problems. I did have to buy an 8000 baht insurance policy. The internet banking seems to be working without issue. Maybe you are unlucky with the branch?
I used to bank with KTB, I would avoid them. The last I knew they shutdown the web portal so you can only use the phone app.
I just applied for and received my METV from the Thai Embassy Washington DC.. You can do an evisa - no reason to travel there.
I have been nearly ten years and most of that was on tourist visas. There is no reason you can't stay a year. Once you get here and start to talk to others you'll understand more.
I would recommend applying for an METV, plan to stay 9 months, and leave your plans open-ended from there. I think you will find it makes more sense once your here.