Olympus OMD EM-5 body + the 45mm as my only lens (is it possible?)

The most common 35mm equivalent focal lengths have traditionally been 35mm and 50mm and in between.

The famous Rolliflex TLR had a default field of view that was in between those two. (In fact, if you use the 17mm with your m43 camera and then crop to a square, this will come close to the Rolliflex FOV).

50mm (or 25mm in m43) is better if you are going to be doing a lot of portraits. 35mm (or 17mm in m43) is better if you are mostly going to be doing documentary photography.

The 45mm lens (90mm in 35mm equivalent) is a WEIRD and limiting focal length for your only lens.

The OP seems to be overvaluing the sharpness of the lens, as if sharpness is the only thing important to taking a picture.

If super-high resolution is the only thing the OP cares about, he'd probably be better off with the Sigma DP2M Merill camera.