all visa applications are online now, no embassy visit unless you are called in for an interview. You choose the particular embassy to apply online according to where you are physically located.
Initially a 6 month course will suffice. If you border bounce at 180 days you won't need to prove ongoing activity, but if you do an in country extension you will need to update and prove basically all the initial application criteria, plus some.
Regardless, the business surely is registered in some jurisdiction, go there and screenshot/link the registration, same with the companies website About page or mission statement page etc. Get creative and innovative.
the e-visa application website specifically tells you to print out and present the paper upon entry and to airlines if requested. The embassy told me as much at the end of my interview. Your circumstances are not great advice to the average recipient. Especially let's say the police stop you and want to see your visa, all you'll be able to provide is an entry stamp.
In your case, if using your husband for sponsorship you'd need marriage certificate, and likely a million baht in his bank account, even though he's not a DTV user, he's having to support 2 people. Pick a nearby embassy that only requires 3 months of the funding requirements. Bottomline is you need to present a believable stable financial situation.