Have fun in bleau, if it's your first time, be prepared to take a beating ;) Thats perfectly normal.
I don't know how the ratings are in the UK but our general rule of thumb was: Take your usual rating, subtract 1 and thats the bleau rating. Of course, this might be a little exaggerated, but going down half to 2/3 of grade seems fairly reasonable (compared to something "universal" like Moonboard ratings). (Of course ratings as always are highly subjective).
As for locations, just pick any. There are so many boulders in the area that you will always find something for you grade and liking and if not, the next area is just a 10 min walk away. I've always been partial to the Trois Pignon area especially the 95.2 area. The "best" area realy depends on your style and preferences.
As for guides, the german "Bleau en Bloc" is pretty good but I don't know if there is a translation available. bleau.info is a nice list of allmost all problems in all regions.