"Micro braids" mean different things to different people. I call my braids "micro" or "singles' interchangeably because I think they are tiny, hence micro; but then I see what I'd call "nano braids" being called "micro" and so I start to think mine have got to be just singles. I don't think they can be called medium coz to me medium are a little bigger.
My belief is if you get your braids any smaller than what I have here
...then you risk getting damage from them. Also I hope you can see that the section to which the additional hair is added is made up of more than just two hairs (<--a slight exaggeration). Whoever is doing your braids has got to use less additional hair than the thickness of that section of your own. I think you get a good idea of how much extension hair I add per section when you look at the braid I have undone below and then look at the freshly braided hair. The finished product looks so much thinner than that section of my hair was. That's because I add very little hair so that the change in thickness of the braid due to added hair is very subtle.
But I think you can be assured of having a positive experience with braids by either going to someone who's helped someone else grow their hair w/o problems (ie Do your homework: find someone on this forum or elsewhere with a success story and who lives in your area) and go to the stylist to whom they owe their success. Or better yet, learn to do your own braids because you can gauge how firmly to braid--what feels comfortable--and also when you need to redo a braid and get to it pronto.
I have had a positive experience wearing my idea of micro braids (first pic) but I think it's because I do them myself and therefore give my hair the type of TLC only the owner could give