Yes, there can be a career in TEFL. Many people stay in it for decades. You have to be prepared and understand the market of the country(ies) where you go.
As for a career progression, that can be case by case. Start at whatever bottom rung there is for the country you choose (in Japan, it's ALT for JET programme or dispatch agencie, or it's conversation school teacher).
After that, people can move up to full-time solo teacher (not ALT), start their own business, or whatever, depending on their credentials.
I moved up from conversation school to private HS to university.
Some people will get into management at conversation schools, others become trainers. Security and stability all depend on you and where you want to work. "Comfortable living" is relative. You'll have to explain that more, and maybe tell us what countries interest you.