I've used the 19mm f/2.8 from Sigma on my OM-D and found it to be an excellent and inexpensive lens. It was the first one I bought after the kit zoom. Since the EPL5 uses the same sensor as the EM5, I am going to guess you would get equivalently good performance with it.
In case it helps, here are links to some photos I posted using the Sigma lens on the m4/3 body when I first got it. One thing that I wasn't expecting was the good close-up performance (even though it's not really a macro lens).http://gerafotografija.wordpress.com/2012/10/09/closeup-nature-photos-with-the-sigma-19mm2-8/http://gerafotografija.wordpress.com/2012/09/25/some-pictures-from-walking-around-town-with-a-new-lens-this-weekend/
Although I saved up and got the Summilux 25mm f/1.4 instead of the Sigma 30mm, I was definitely considering it after such a good experience with my first Sigma lens.
One thing I found really useful was using the Oly 12-50 kit zoom for a couple months, then sorting through my favorite photos and figuring out what focal lengths I was using the most. In my case, I initially tended to use the extremes (24mm and 100mm FF equivalent) the most since I was getting a lot of either portraits or group people pictures with family and friends. Later, when I started going for street shots, I starting using the 20-30 range more (40-50mm equivalent).
If you already have a D800, you are all set for lanscapes and nature photos. However, you may find yourself liking putting the lightweight 75-300 zoom in your bag for wildlife, and stitching together panoramas with relatively tiny primes like the 45mm f/1.8 or 60mm f/2.8 in your pocket.
Keep in mind that you're probably going to stick to lower ISO than with the d800, and won't have as much extra resolution for cropping in post. I love the Oly output at 200-400 ISO, and can work with it in color up to around 800 before the noise starts to be a problem (double that for monochrome).
One last thing. Both the 12-50 zoom and the 60mm 2.8 macro have the same level of weathersealing as the magnesium alloy body on the OMD. If I remember correctly, the EPL5 isn't drip and dust proof like the higher emd model.
Hope this helps. There are a lot of good choices out there right now, and more coming. So, if you're not sure exactly what you need, wait a bit, and you're almost sure to find something you want being developed by the photo industry.