Your salary depends entirely on what sort of job you land and what you do and how fast you get promoted.
Salaries for engineers vary widely by geography as well. So California has some of the highest pay for very young engineers. You may want to get half way through an engineering degree before you worry about whether you want or need an MBA. Many engineers find masters degrees in CS or EE to be much more helpful than an MBA. MBA’s do case studies, may learn financial math, may study accouting, or marketing or may study supply chain management.
MBAs are also useful if you want to get into the top investment banking jobs, for instance, and some GT grads can do that straight away. Goldman Sachs hires a lot of graduates from Wharton, which is U of Penn, who have undergrad degrees in engineering/CS, as well as Harvard, Stanford and MIT MBA students.
MIT’s Sloan School may be a good fit, as its more quantitative.
MBA graduates might choose to work at Delloitte, or Price Waterhouse or any number of management consulting firms. Many positions in management consulting don’t care if you do an engineering degree at all. You can major in economics or history and still get a great job after a great MBA, with good grades, at any top management consulting firm. If you take that job, you will live out of a suitcase, and travel to clients for a month at a time. You will not see your spouse very much but make a ton of money if thats what you want. However that is NOT an engineering career.
Engineering careers involve design, manufacturing or R&D. Some engineers choose sales and marketing.
Engineering involves building something, whether it be hardware, software or a bridge.
The companies you mention, Google , Facebook, Twitter, hire both engineers and MBAs. Those are entirely different job functions. Read more about MBAs to learn more. YOu can also get a masters degree in accounting, and get very highly payed. Accountants balance the books for high tech and other types of firms. Its a complex function and involves a lot of responsibility to get this exactly correct, and it matters for taxes as well as stock holders.
Your question about industrial versus CS, again, its what interests you. Read on GT website about both majors now so you know what you want. At Georgia Tech, the GPA transfer criteria for CS is 3.3, and the transfer for all other majors is 3.0.
The CS group at GT is very competitive. They are taking more and more out of state students. Certainly Google, Facebook and Twitter are more focused on coding and software than manufacturing, but they may do some manufacturing in foreign countries like Mexico, SW Asia and China. They need US engineers that understand manufacturing, but that does involve a lot of overseas travel if manufacturing sites are abroad.