A bank statement from the last 3 months, showing sufficient funds in your account to cover the 800,000 baht, currently dated (downloaded from online) does the job too.
You can reduce PDF file sizes easily (and massively) by using Acrobat. I’m sure there are other programs that will do this too or you could get someone with licensed Acrobat to do it for you, if you haven’t got a licence yourself.
Head of village will likely pose in a photo with you of the house. I suppose this is to establish that you haven't caused any controversay locally. First stop should be the local Amphur to confirm their exact requirements rather than relying on heresay and whatiferey. Best to have wife/local Thai speaker with you to obtain the correct requirements.
You need to get your passport certified at the British Embassy. To do it in person, there is currently about a 2 week waiting list. First you must register your details and pay the £25 fee. They will then send a link so you can make an appointment. Pretty sure there is a courier/postage option too but I didn't pay it any heed as I will attend in person. Confirmed all this with the local Amphur two days ago and they were very helpful. New passport in my case and not the one certified when I got married a couple of years ago.