Z 85 f1.8 lens

The Z 85mm f/1.8 is a terrific lens - sharper than any 85mm lens ever released by Nikon and with a nice bokeh. It's a relatively large lens - but that because optics were the priority. Probably the question for you is whether you really want this focal length. On a DX camera, it's the equivalent of 128mm, and that's a relatively long lens for portraits and general use.

The alternative is probably the Z 50mm f/1.8. It's generally regarded as the best 50mm lens Nikon has ever produced, and is at the level of the best 50mm lenses from any company at any price. The effective focal length - 75mm - is probably more typical of a portrait lens. It's slightly long for a normal lens, but that's a matter of style and personal choice.

The lens that is more typical of a "normal lens" is likely the Z 35mm f/1.8. The effective focal length on the Z50 is 53mm, and that's more commonly considered a "normal".

You can't go wrong with any of these lenses. They are all relatively fast, very flexible, and would be good choices for either a Z50 or any future camera. The optics are all very good to excellent. And all can be used wide open with good results, or stopped down as needed.

Don't forget, you can use the FTZ and any older prime lens - even manual focus lenses. With focus peaking, old primes are a lot more fun to shoot and manual focus is easy. Many of them are very small, and while the sharpness does not match the most recent versions, they have a character that is different and makes using the lenses lots of fun.