Would you bother with the 12mm F2, 17mm f1.8 or 45mm f1.8 if you had the 12-40 f2.8 Pro?

I bought the EM-1 first (with adapter), the 17 1.8mm (on sale), and the 12-40 (on sale).

I then purchased the 45mm used, the 75mm new (on sale) and the 12mm used (40% price). I also sprang for the 40-150 Pro and TC new!  I then got the 25mm 1.8 used. I could very nearly sell all my m4/3 lenses for 90% of what I paid for them after having them for almost two years.

I use the zooms mostly for outdoorsy stuff that requires either weather sealing, or zoom versatility. (When I had the E-3/5, the 12-60 and 50-200 were my go-to lenses)

Now I usually take the primes with me on a daily basis, as they are lighter, faster, and just fit the EM-1 so nicely. The zooms stay in the trunk just in case.

The 12, 17, 25, 45, and 75 are really good lenses, and I find the faster F stop significant, especially in the evenings, and for shooting my grandkiddies.

The only reason I would get rid of any of my lenses is that I have too many, and can never decide which ones I should take. Maybe fewer lenses would be better.

I agree with the others that have recommended the 45mm 1.8. This is probably the best value prime. The 17mm would be next, as the build quality, pull-back-to-focus, and rendering, make this an excellent all around lens.

The 12, while very sharp (my copy), is probably not necessary if you have the 12-40.

The other prime you should really consider is the 75mm. It replaces the 40-150 (pro or not) for a lot of situations, and complements the 12-40 perfectly. I would take this lens over the 45mm for focal lengths over 40mm if I had to choose just one.