I always rate https://www.meteoblue.com/. Does everything you've asked for and is pretty accurate too. Some of the more esoteric forecasts are subscription only
Its very good, particularly when abroad too. IIRC I think its French. Never failed me over in Europe...
I do the same. Low wind speed, high humidity, low visibility and chances are you'll find some. Plus knowing the area, and if it's a likely place to mist up - low ground, ponds/lakes etc.I use met office, if it says visibility moderate or poor, chances are there is mist and/or fog about.
Don't ask me, I drove a 7 hour round trip on Sunday because I thought the forecast looked perfect for fog/mist in the hope valley!
There was very high humidity (but not 100% this is important), the temperature and dew point were very close, low wind speed, rain the previous evening and completely clear skies.
Didn't check the visibility though I'll remember that one for future...
Not a single wisp of mist, hardly any cloud apart from a thin bank on the eastern horizon. Typical.