We have been at Bled, it is a very good site, nicely situated on the lake shore. The restaraunt is excellent. We were there in late may/june so cant help with the August weather, we had temps of 25-28C, followed by thunder (we are always followed by thunder)!. There were no Motorway vignettes when we were there (2 yrs ago) but they are starting very soon, I think. I would not hesitate to go back!
all the best
JimF