So thanks for dropping by dude. You ask some tough questions - not only because they are tough, but because they are so long-term. which is of course great, because by thinking about them now you can best prepare the future.
So first things first... keep on trying to get into MC if that is truly what you want. But be careful too. You don't want to get into a situation where you become obsessed with MC to the point that you become disappointed/ frustrated with what you are actually doing. Whatever it is you do do, you want to make sure that you are doing the BEST you possibly can. Ultimately people go to Bschool from ALL fields, but high performance and quick promotions at your job are maybe the most important things in your profile.
Second is the GMAT. MC firms will also look at your GMAT. So if it's under 700, you will have a very hard time getting in the big firms, and it will be equally hard to get into top Bschools. But make sure you take the GMAT with plenty of leeway (a year and a half before applying is nice) so that if things don't go well, you can retake.
Next - make sure you have at least one good solid serious community service post. Leadership is a bonus.
With this three things (plus hopefully some extras) top schools from which MC firms recruit will be open to you. The Top 10 will likely be out of range due to your UG grades (of course you can rectify this by doing totally amazing at work). As for getting an MS - only if you need/want the MS. It won't cover up your UG grades at any rate, so if you want the knowledge go for it... otherwise you should think about seeking another path.
Hopefully this will get you started.
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