Pentax make a small DSLR(s) - (the Kx?), and their glass is (very) good and reasonably priced - you can also use all Pentax MF glass from years back - (M screw fitting included) - cheap and good off Ebay
For use as a main camera the lack of a view finder is a big negative for me and I do find the controls on the EP-1 and to a lessor extent the G1, not (nearly) as good as on the DSLRs, (I have a Nikon and a Pentax). Trying to frame with a LCD, particularly in good daylight is not a great experience
The physical size is a big positive for M43, but as your main camera, I personally would go for a G1 or it's latest replacement rather than the EP or GF
M43 is fine with the fixed 17mm and 20mm lenses (and 45mm), but once you get into telephoto territory I have found the available lens to be less satisfying
don't get me wrong, I like my M43 stuff - but they do have drawbacks which offset their size - "they are what they are"
(my comments are versus a conventional DSLR)
Hope it helps