Well they are the gatekeepers to that. If you don’t fulfil their requirements, they won’t grant you access. If the Thailand side immigration ask you questions, that’s pretty easy to deal with by, for eg, booking a longer stay somewhere if that’s a requirement. It often depends on the individual immigration officer you get. I hardly think they are going to put you on the next plane back.
BTW if you're applying in London, even more reason to enquire directly from them. Speaking to other over the years who have applied elsewhere (esp in the US) the London Embassy is a pita to deal with and is v picky/random about requirements, in my experience.
Personally I'd seek advice from the Embassy where I'm applying for the visa. Requirements vary from Embassy to Embassy and they also change frequently. You'll get much more accurate info from the primary source than from an expat FB group.
Sure. I don’t really know why you’re getting so hung up on TM30, it’s just more or less the same as hotels registering your passport. It’s just part of the process of registering people in country. I just mention an apartment because I think you need to specify and provide evidence of booking for at least a month post AQ on the application. If you want to pay for a hotel for a month, that’s up to you but apartment will likely be cheaper, for reasons given.
I think you'd probably be ok just giving the first month (and if that's not the case, the Embassy will inform you). Personally I'd book a cheap condo on a monthly lease. That's what I did when I first visited Thailand. When you check in you can request a copy of the TM30 (it's the landlord's obligation to fill out and only really apply to apartments, not hotels so it doesn't matter as you travel. I've lived in Thailand for around 6 months of the year for the last 6 years and have never filled in a TM28, or know someone who has. I've also never been asked for a TM30 but do always request a copy). If you want to travel after 2 weeks, you'll have to wave the last 2 weeks in rent but monthly apartment rates are often not that much more expensive than booking 2 weeks. There's a huge number of discounted apartments atm. Settling in and travelling in Thailand is incredibly easy, even in the current situation so you really shouldn't have any problems as long as you do everything by the book.