Sue -
I made a similar switch from Pentax DSLR's to micro 4/3 cameras a few years ago - mainly because of weight - what really got to me was taking some long multi-hour treks in a national park and lugging my wonderful (I still miss it) Pentax around and thinking with each step that it was getting heavier and heavier and heavier -
So I switched initially to Olympus and then, later on, for various reasons, to some Panasonic/Lumix'es as well. The weight savings floored me. Which is not to say that I don't (still) miss my old K200D because in some ways I do - it was a phenomenal camera. But to be honest, several of my Olympuses (is the plural of Olympuses....Olympi?) and some of my Lumixes are phenomenal cameras as well. My current favorite is a GX7 which somehow seemed to hit a sweet spot for me in terms of usability, feel, and photographer-friendliness. And, yes, all the mu-43 lenses are interchangeable - I've used my micro 4/3 lenses on a variety of different Olympus & Lumix bodies, with excellent results.
To second Nic's earlier answer, the VF-2 should be compatible with the E-P5 - and it's quite a fine viewfinder in my opinion.
The only other camera that I would suggest adding to your list is the E-M10. Though it's the 'baby brother' to the E-M5, it's quite an amazing camera in its own right and its combination of size and weight (very small), usability (very high) and general cool design ranks it probably at the top of my favorite Olympus cameras. And, no, I don't have one - but were I to get another micro 4/3 body, it would probably be at the top of my list.
Though, I must say, Pentax lenses are second to none. The good news is that Pentax K-mount to micro 4/3 adapters are relatively inexpensive (some of them, anyway) and quite good; I bought one which allows me to use a wonderful old analog Pentax lens, a 50mm f/1.7, which though it's technically now a manual-focus 'legacy' lens, still pairs wonderfully with my current Lumixes.