1. Does anyone have this body and use it for the scenarios mentioned and can comment on if it's as good as it's reported to be ?
2. I understand that you have 4k up to to 60P oversampled from 6k and it's supposed to look fantastic - is that the case ?
Sorry do not have the body myself... but all reviews since A6500 days say its one of the sharpest 4K output, so I imagine it'll look good as far as sharpness goes.
3. Does the single card slot worry anyone (I've not had a camera except the RX100 with a single card slot in years) ?
Doesn't necessarily worry me a huge lot but I'd suggest backing up cards as soon as possible like at the end of the day.
Then again I only shoot for personally, not professionally. So if my card dies, I lose max one day of shooting and there are no law suits etc.
4. What would a nice pair (or trio) of general purpose lenses for this body. They don't need to be the latest and greatest F1.4 or F2.8 units as like I say, the camera will typically be used as a go anywhere lightweight package (or a B Roll camera). I was thinking about the Sony 10-20 PZ lens for wide angle, the 18-135mm as a general purpose walkabout lens, and (possibly) the 70-350 OSS as a lightweight telephoto option. However as I know nothing about Sony lenses I'm not sure of the optical performance of these and if they are decent enough or not ?
70-350mm is one of my favourites lenses, there is nothing like it on any other mount. Its relatively small, really sharp at long end with really good AF.
I'd shoot Sony APS-C just for this lens! used it as my travel lens for a couple years on my FF bodies (in APS-C mode of course).
10-20mm f4 is very good too.... once again nothing like it on any other mount
As for primes I suggest looking at sigma f1.4 lenses - 16mm f1.4, 23mm f1.4, 30mm f1.4, 56mm f1.4. The 16mm is a bit big but the rest are small lenses.
There's also Sony's 11mm f1.8 which I had and is a bargain in terms of performance to price, and the 15mm f1.4 G looks good too and lot smaller than sigma 16mm f1.4.
And there are of course a plethora of smaller f1.8-f2 FF primes from samyang, sigma, sony which will all work on APS-C
for normal zooms I'd pick up a Sony 16-55mm f2.8 if you can afford it, if not 18-135mm is good and so is 18-105mm f4 PZ for video work.
There is also a sigma 18-50mm f2.8 thats really small and good enough for 4K work but doesn't review so well on high res APS-C sensor like on Fuji XT5.
5. Is the relatively low res (2.36mp) viewfinder a deal breaker or OK ?
not for me, could be for you. I suggest trying it.
if I were to make a video centric kit with A6700 myself my choices would be - Sony 10-20mm f4, 15mm f1.4 G, 16-55mm f2.8, 70-350mm and Sigma 56mm f1.4