Depends where you live and the life style you want. Her 1600 pounds is 2000 dollars and for a single person that is fair. I pay for 2, rent an apartment, run a truck and a scooter, live in BKK, support the family and travel. We do that on 3000 dollars a month plus the odd bigger spend.
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.