you need to be licensed in Thailand to do that. Also concerning your husband, any kind of commercial driving, including bus driving, is restricted for Thais only.
Yes, a medical certificate is required to get a Thai driver's license. You are being scammed though, as you can not get a legal Thai driver's license online. With these online scams you'll never know it is a fake license until you get stopped by the police, and then you can go to jail, and be deported for using counterfeit documents. Be fully aware of this.
the grey area to protect your ownership is in the corporate voting rights of the company stock the Thai partners own. It can, and is, set up so they don't have voting control of the business.
just so it is not a tour guide, as that is a restricted occupation. Each work permit a company sponsors requires what I listed registered capital wise. There is no way around that.
To get a work permit the business must have at least bt2million in registered capital, and that you hire at least 4 Thai employees you pay social security, and wages on. Then you can only own 49% of the business yourself. The rest must be Thais, and they've started cracking down on proxy Thai owners. Remember, you can not legally do any work without a work permit.
I personally do not know what immigration's reaction will be when you don't have your old passport in your case. All comments made in that respect were assuming you still had your old passport. If it was an emergency travel passport then yes, but in your case I have no idea how immigration will react at the airport.