If you want to do portraiture, you need ff, a sony a7 would be a better choice and they're currently £600 on amazon UK brand new. The a7 is still under 500g, marginally heavier than the xe3 and xt30, but less than the xt or xpro or xh range.
And have you checked the price of fuji flashes, if you want hss, you will be spending about $500 last i checked. I got 3 strobes and a master commander for that price on sony.
And no, a 75mm f2.8 equivalent as your only lens is a horrible choice. If you're going to have just a single prime lens, i would always go for a 35mm on full frame. The samyang 35mm 2.8 is spectacular for the money and weighs only 80g, it's my goto if I want a light holiday cam, or the tamron 28-75 2.8 if I want something a bit more versatile.
Admittedly the af is not great on the first a7, but as an art photographers tool it is without comparison at this size and weight.