They only care about your money and how much they will charge you for the service, you can do 90% of the work your self
Frist thing is how old are you if under 50 you can cross some off the list
How much money can you afford to pay for the visa application, so you just need to look into the rules and regulations for your own age and the limits for your cash flow will be very important, because that's what it's all about money 💰
Yes you will have to make a new tm30, if that's what you normally do for your immigration office as every immigration office is different some say don't worry and some say we want one each time you go on holiday
Don't do it you will never make any money on the house, the quality of the building is very bad compared to the UK
As for you starting your own business in Thailand to own a house it's going to cost you a fortune for lawyer's and you have thai employees at least 4 working for you
You would be better to get the retirement visa's
For your frist year and rent a condo and look at what you have to do with the thai immigration requirements involved every year and report to them every 90 days, you need to read the rules before you travel,
But Don't SALE your home in the UK just incase you don't want to live in Thailand after the move,
Have a good look around and find out what information you can
There are many different options available for the visa application
It all depends on your money situation so please stop and think about it as Thailand is not as wonderful as the holiday you have had here, And do not trust anyone or agent that makes wonderful promises to you,