If you are planning to apply to bachelor programs, and then to medical school, DO NOT take Step 1 beforehand. Most states in the US have a time period during which all three step exams much be taken. If you have a long break between Step 1 and Step 2 (this would likely be a 7-8 year gap if you take it in the 3rd or 4th year of medical school), you will be at risk for not finishing all exams on time. Besides that, the average score for Step 1 increases almost every year. A good score today would likely be a very mediocre score by the time your residency comes.
As for transferring credits to an undergraduate university, you may not get as many credits accepted as you expect. And you would need some sort of US clinical experience before you apply so I think 2 years is a little optimistic...not to mention the year it takes for the application itself.
You are setting yourself a very hard path. Is there a reason you want to practice in the US rather than your home country? You are realistically looking at an extra 6-7 years just to get back to where you are now.