One nice thing with the OMS BP is it is the same pattern as the more expensive Halcyon BP. This allows you to use the Halcyon lift bag pocket/plate cover on the OMS plate. I have 3 OMS plates all with the Halcyon accessory (2 steel, 1 aluminum). I also have 1 DR BP, which (ironically) is the one I almost always use these days. It is a little bigger and seems more solid. I put a lift bag pocket outboard on each side since the Halcyon cover/pocet does not fit the DR hole pattern.
As for wings, I have exclusively DR wings. I have 2 Classics (double), 1 Trek (single/double), and 1 Venture (long single). I also had a DR Rec Wing, which I sold, but wouldn’t mind still having. I’ve tried OMS wings, but find them to be oversized and bulky. I also don’t like the tight bungee strapping that is needed to keep the gialnt doubles wings in check (but also cause the wing to fully force-deflate if it gets even a tiny puncture. I would also consider an OxyCheq single wing for a smaller single tank.
With respect to harness, I strongly recommend simple 2 in webbing. It is cheap, simple, and easily replaceable and makes just as comfortable a harness as any of the fancy sewn ones with all the extra buckles, snaps, rings, and pads (unless you dive nude, then the padding might be nice to have).