Suggestion for E-M5 (free) accessory

I am coming from P&S with manual controls and while I was first considering upgrading to a G12 or G1X, I am more and more convinced by the OM-D E-M5.

I tried to never use the flash because of how bad it is generally and with the E-M5, I should have better chance not to use it (ISO-wise). I do not own any legacy lens or regular Four Third lenses.

So, I am debating which accessory to get along with the camera (the kit lens I'd get is the 12-50).

The FL-300R would enable me to use the flash sometimes, but I get the feeling that if I start using it frequently, I will want to upgrade it to the FL-600R for a much more potent flash.

Both of the adapters (MMF-3 and MF-2) seem interesting because they open the door for other (hopefully cheaper or at least better) lenses. But its not an accessory I'd normally buy and I would basicly settle for M43 lenses if I do not have the proper adapter.

Writting this, I feel like I should get the flash since it is sure to get some use at some point in time, but maybe I am neglecting something regarding the adapters and the used market for lenses.

So, based on my situation, what would you suggest ?