There's no right or wrong way, just the one that suits your situation best. The cheapest modular route to a multi engine CPL/IR is to go for a single engine CPL/IR first, so the two options above aren't either/or. It's an easy decision - to for option A then consider your options. I wouldn't recommend flight instruction full time. Maybe as a part-time gig but you can't really make money from it like a 'proper' job. If you're young, free and single and don't need to hold down a job, then I'd still recommend training to CFI in the US then coming home with 1000 hours - assuming you can still get a 2 year visa. With literal interpretation of part 61 you only need 100 hours in an airplane. Its the cheapest option of them all...