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Have the Fujifilm X-S10 , one zoom and 3 fixed lenses. I'm a big fan of IBIS paired with the fixed lenses which ruled out the A7C for me (along with the extra cost). Saying that, Sony do offer some small and competitive FF lenses, the FE 50mm f1.8 and at £165 is cheaper and the same weight as the Fujifilm 35mm f1.4.
Stick the lenses you'll want into https://camerasize.com/compact/#858.580,864.408,ha,t and get a sense of how much smaller it is. I'm finding mirrorless small enough to take out more than I did my Canon 40D DSLR, while being more fun to use.
I'd probably have a couple of fixed focal lengths and a zoom lens. I'm not so fussed about the film settings on the X100T. all of that can be done in post anyway.
Sony A7C looks like it can do everything the D800 can do and is a fraction of the size. Still unsure though.