I have owned EM1, EM1.2, OM1 (current), OM5 (current). The OM5 is like an EM1.3 in an EM5.3 body, with some minor function reductions and only 1 card slot.
There was a big jump in IQ from EM1 to EM1.2, larger than the resolution increase would explain. After that pretty much all the 20Mpix bodies have the same IQ. There is a small improvement in colour accuracy in deep shadows with the OM1/OM3 sensor. IBIS in the OM1 is better and better still in the mk ii, but it’s better than a modern Sony in the OM5, so pretty good since the EM1.3.
The stacked sensors in the OM1/OM3 have a trivial DR penalty. Olympus/OM changed sensor calibration settings from model to model, so you can ignore ISO in terms of exact DR, except at base ISO. The EM1.2 was famous for having a true base ISO of around 120. After that it’s been a lot closer to 200.
If you are a jpeg shooter, the OM1/OM3 in-camera AI noise reduction is pretty good. It’s not quite as good as DxO DeepPrime, but still impressive. Bodies with handheld Hi-Res stacking can reduce noise in low light by producing stacked jpegs or pseudo-RAWs. That can be quite helpful.
If you can manage without an EVF and want a popup flash, the EP7 has IBIS but only CDAF.
Unfortunately, small cameras are selling well at the moment, but you still see discounts on white EP7 kits and OM5 kits (with the rather wonderful 12-45/4) from time to time. OM also advertise “refurbs”, which look rather like open box returns that they have checked over.
Signing up to the OM newsletter gives you notice of offers and sometimes an additional discount code. If OM are launching a new product, there will be tryout sessions with a lot of lenses at stores. You get a voucher for attending which can go towards a spare battery or anything else.
Might be worth considering the Panasonic G100D as well.
Hope that helps.
TL
R Sounds like a used EM1.2 might suit but sometimes an OM5 plus 12-45/4 kit is cheaper than buying a used body and lens separately.A
For sure 
for me.
sold 1, swapped another.
