Olympus compatible off camera flash for street work?

Hmm, that's low GN?  ...short answer is you will need to experiment with the daylight.  No problem with using small diffusers on standard stobes, very portable, used hand-held for your application, works great for fill-in especially outdoors.

First issue (outdoors) will be shutter speeds required and the second will be the trigger method, and the third will be whether you wish for TTL or Manual control.  I do use an FL-LM3 to optically trigger various flashes (mainly Nissin's) because i can turn down the optical trigger power and articulate the LM3 head towards the main flash.  However i am perfecting that method for indoors work and it still means using some on-camera flash whether i want it or not ...but i have not yet tried this method in outdoors daylight.

True radio triggers might be the better answer as long as you are ok with Manual?  The tiny little Cube radio triggers (simple TX & RX) are likely to be more reliable outdoors than Optical.  For this method i use Captur, and they are proving to be very reliable.  (btw the Captur doubles-up in the other direction for a true-radio, remote shutter release)

However, when i do get around to moving outdoors, i imagine i will also want to experiment with HSS in-order to balance the ambient light.  Hence i am watching Godox (from afar) for a true radio solution but for-now that still means a 'two-box' solution, albeit their flashes are very good value.  Hence until true radio is developed for an MFT camera body, i may just end-up purchasing a pair of Godox.

Meanwhile i am enjoying the challenge of trying to perfect off-camera manual control over my Captur's radio link.