So what would you advise for the Oly E-M10 (with grip)?

Rather than an advise, I'll share my thoughts on my lenses for the E-M10, and prospective gear.

I consider myself an amateur photographer. I mainly shoot nature, street and portraits, but ocassionally I do video, mainly electronic devices teardowns. I don't look for excellent video quality, but appreciate good detail in close ups. This results in a very broad range of needs, as you may guess. Currently I own:

Olympus M.ZUIKO DIGITAL 14-42mm 1:3.5-5.6 II R
Sigma 30mm f2.8 DN Lens
Olympus M.ZUIKO DIGITAL ED 40-150mm 1:4.0-5.6 R

I've found these lenses to be excellent low-budget options, very well suited for novices as they are lightweight, sharp and responsive. But, of course, they have their limitations. For example, would not recommend any of them for night or low light photography. You won't get that creamy bokeh of the faster, longer primes. You can get pretty decent macro shots with the 40-150mm and the 30mm, considering they are not macro lenses, but if you want real macro capabilities, they are not for you. These lenses are not designed for full-manual operation, specially in terms of MF.

Based on my needs and the limitations of these lenses, I plan to purchase the following:

Zhongyi Mitakon 42.5mm f1.2: This combination of focal length and aperture are great for narrow DoF and low light. I want to develop my full-manual skills, so this lens seems to be a good starting point. Some people simply don't want to mess up with manual, and that's ok, and depends only on personal preferences. Other excellent option, is the Oly 45mm, which is, in my opinion, the best AF lens for portrait, or the Nocticron 42.5mm, but that is totally out of my budget.
Olympus M.ZUIKO DIGITAL ED 60mm f2.8 Macro: MFT system is lacking native macro lenses, so this lens has little to no competition (I can only remember a japanese macro lens branded Yasuhara or something close to that). I would get this lens purely for technical photography of electronic devices.

My final word is that everyone has an ideal lineup depending on personal preferences and needs.

 

Anti-GAS advice: do not but anything unless you know that you need it (and why). Done.

I think you already have the best lens for shallow DoF: no other prime is going to give you much more. The 45 could be a little more "usable" indoor but you already have two long lenses. Oly 25/1.8? If you are not into lens changing I would avoid more primes.

The 12-40 can give you the 12mm and is also a "casual macro" lens and is one of the best lenses around. The weight is not that different from the 75-300 but it is shorter: it's going to be quite front heavy. Another option could be the smaller and lighter Pana 12-35/2.8 (and it's brother 35-100).

http://camerasize.com/compact/#521.412,521.346,521.336,ha,t

I think you wont see much difference from the zoom you have now unless you print big or pixel peep or have a good eye for barrelling, CA, corner softness, things hard to spot on a monitor. It's going to give you one or two extra stops for low light shots.

For macro the 60 is another thing but I mean "real macro": tripod, lights, ultra shallow DoF, etc. I do not know if you are willing to do it (I'm not).

My advice: if you are suffering, and I mean it, in low light go for the 12-40/12-35 otherwise wait for the next GAS attack. If you like to shoot with the 75 but you find it is too long consider a shorter prime, 45 or 25.

 

The grip makes a huge difference. One of the best accessories I've ever bought for a camera.
I use the 12-40 almost exclusively; it's bright, focusses quickly, focusses very close and is razor sharp. My next lens will probably be the 40-150 f2.8. It's a lot smaller than the Canon 70-200 and covers a narrower field of view (9.25 deg.) at the long end than the Canon (12.3 deg.). The Canon lens is almost exactly twice as heavy and I believe it's a lot more money.

 

I have 6 lenses (plus 3 adapted manual focus) and the 12-40 is the one I use most, followed by the 40-150. The 75 is the only one I'd consider to buy right now but I'm quite sure I won't use it enough.

For manual focus you can configure the Fn buttons or the rec buttons to activate the magnify or peaking. The magnify is also available in the "multi option" function.
And if you are into camera configuration you can save this config to a specific MySet to use for manual focus.

The 40-150 is as new as it gets: the price is going to drop.

 

Having owned a number of primes and zooms (still have 7 native zooms/primes and about 10 adapted primes), I can say that for me the 12-40 f2.8 is by far the most versatile and most used lens. It is awesome for sharpness, rendition, low light, and is weather sealed and focuses almost like a macro lens.... I recommend the 12-40 f2.8 without reservations.

(and yes, I had the 12-35 f2.8 as well)