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I would start with the lens you have tried and love. The 50MP is very different, sharper, but with much less attractive boke and more neutral rendering. I have both and prefer the Planar. The price is also very attractive.
Once you have that, you might look at the 35s. I prefer the f/1.4, but it is huge and expensive, and quite hard to focus. The 35/2 is also very nice, but with less subtle rendering, but more obvious 3D.
The 85/1.4 is great, but has focus shift and is hard to focus as well. For people at close range this lens requires quite fine control.
The 100/2 also has beautiful rendering, and has 1:2 near-macro range ability. This might make a nice second or third lens, or perhaps the 135/2 if you can use the range and don't do macro.
The 21/2.8 is legendary, but if you don't shoot that wide, then perhaps it is pointless. The 25/2 is meant to be great, but I don't own it and cannot verify that. In any case, it sits in the same spot as your existing lens.
The 28/2 has a mixed reputation. It has field curvature, which can cause boke problems in the corners, but it has this very gentle, beautiful boke for certain subject/background ranges, and I love mine. It has been called an artist's lens, not implying that anyone who doesn't like it isn't an artist, of course, but giving some sense that it isn't great for purely technical matter, perhaps.