In fact, it's probably better to apply in countries outside of where your employment is based in case they impose strange requirements like extra documentation related to your work, for instance in Myanmar, they're asking for proof of registration with government authorities or something to that effect, which is not something many people can prove. An applicant working for a Burmese entity but applying in Laos or Vietnam won't be asked for such documentation and thus has a higher chance of success.
Forget agencies. They charge an arm and a leg and are why consulates are making it more difficult to acquire a DTV. As long as you have 500K to your name and can make it look like you're getting paid regularly then you're halfway there.
English is the world's global language. All Thai embassies and consulates worldwide accept and prefer English or Thai language documents where possible. In most locations, it's required. A few European ones might also accept documents in the language of the application country too, such as German or French.
What country in Africa are you headed to? It sounds like you're coming to America first before traveling out to Thailand. Therefore, if you're going to a yellow fever country, unless it's a requirement for entry to that country you won't have to worry about yellow fever vaccination.
The USA doesn't require it, regardless of where you're coming from and since you'd be traveling to Thailand from the USA, Thailand won't know you've been to a yellow fever country...that is, unless they were to spot a stamp from a yellow fever country in your passport. Having said that as long as more than 10 days have elapsed since leaving a yellow fever country you're good for Thailand as well.
I wouldn't have attached your AMEX statement. Also, Amex isn't widely accepted in Thailand. This is VISA/MasterCard territory and the 3rd most accepted card is UnionPay. 4th is JCB. Amex comes in at a distant 5th.
Anonymous participant 812 You definitely can't. Now with bank accounts being closed for tourist visa holders, your "credit card" will also be, in the unlikely event the bank was stupid enough to give a tourist a "credit card".