There's loads of experts on here who seem to resent if someone wants to have a representative to handle all their immune gration affairs etc., If he wants to pay a rep., to handle it all that's up to him. He's asking for advice not criticism.
You think it's bullshit? Well any monies you have and transfer to your Thai bank account, if your in Thailand more than 179 days, it is liable for tax. Thailand has brought in this rule in line with Western countries.
Airlines don't have open tickets these days. When I was living in Thailand in 2000 to about 2006, you could buy twelve month open tickets with all the airlines I used.
No such thing as required by law. I flew in & out of Thailand dozens & dozens of times on one-way tickets. It's Upto the airline whether they require to see a return ticket, or a ticket onward out of Thailand. I was never ever asked at Thai immigration for a return ticket, only presented my passport and the immigration card, can't remember which TM it was that you were given in-flight.
If in the UK., there's a visa email you can contact and I'm sure they'd advise you whether they'll accept a one-way ticket, if you explain that with your sixty day visa your applying for you'd like to get a thirty day extension whilst in Thailand. Personally I've flown into Thailand dozens of times on one-way tickets and without a visa and got visa exempt thirty days, although this was many years ago.
The proof I was seeking was assuming this was about setting up a Ltd., company with six Thai partners, plus one farang to purchase a property, so the only investor, the farang could protect his investment. If the Thai Government as I've said previously let foreigners buy houses, but put restrictions on how they could sell them, instead of them being able to speculate for profit purposes, then that'd we'd out genuine foreigners from those who'd like to abuse, by buying cheap & selling at a profit.