yes, and I said it is good to proof that money is coming in. That will definetly help the application, i agree and i too had payslips included in my financial proof document. However the OP was asking how much he should monthly earn and there is no such requirement last I checked.
How do they ask for the flights if there is no place for it? Are you sure they are not just asking for your flight numbers? Otherwise if they ask on their site then I would probably combine it with the location proof? You can use something like ilovepdf.com to merge files.
Additional documents have to be provided online but they can also request an in person interview at the embassy.
You risk losing your application if they find out. Some have successfully done this but others have not. I personally would not risk it and would stay in the jurisdiction of the embassy I applied. Choose wisely and good luck.
There is no income requirement so you dont have to proof regular income. However you do need the 500k baht in your personal bank account, not on a business bank account.