No there is a back to back agreement with the UK. If you stay over 179 days then you will probably have to do a tax return. If it is money sent to your wife I doubt any issues as it’s not income.
You can set up a Thai company as an investor in the business but you cannot have more than 49 percent share. The other 51 percent must be a Thai national. From this position you can advise. If the company is profitable you can take a dividend but not a salary and you can not represent the company.
Firstly it is easy enough for you to do yourself. Agents just cost you money. The only thing you need to prove is that you can support you and your wife with your income in the UK. You can have zero in the bank account but you will need to show last 6 months accounts from memory.
Be careful with the word silly reasons. A rejection is a rejection.
Long term visa first ( you can use proof of assets
From your own bank) then agreements for permanent / rented premises and then go to the bank. This way no agent fees or the bank con if selling insurance