First, recognise that my photography is almost always available light - where my standard fudge is to set the camera to "M" and ISO to "Auto-400" (plus manual white balance) - which means it'll use ISO 100 if it can, but roam up to ISO 400 when it needs to. But after some tests today (in my usual 5-10m freediving range! - I'll try to post some tomorrow if I can - bit knackered tonight) ISO 400 can look pretty noisy, particularly if it's at all under-exposed and you're doing much post-processing. So my next tests will be on ISO200 I suspect
With flash - yeah, fix the ISO on 200 max. The Fujis have a habit (if left to themselves) of setting ISO 800 with flash...
I'm still getting the hang of the wide-angle lens. Today's trick was getting a tiny scrap of vignetting in one corner 'cos the "lens hood" thing had twisted a bit. I also did some quick checks on zooming with the lens which seems quite happy at least up to half-way (my video will only zoom half way before it loses focus).