I just obtained a B4, and was told B3 wheels don't fit

I've tried the B3 wheels I have and noticed that they seem to make the B4 wider

. I know the max width is 250mm for any Regionals and Nationals, so I'm asking the Q for club meets (for now!!)
B4 with B4 wheels
Rear (arms level) = around 245mm
front (arms level) = around 245mm
B4 with B3 wheels
Rear (arms level) = around 260mm
Front (arms level) = around 254mm
Now My Q's are
Will the handleing of my B4 be made worst useing the B3 wheels (until I get some more B4 wheels)
Will any other make of wheel fit the B4 axles (front and rear)?
Also with regards to tires/inserts.......what sort will I require for the tracks in the Mid West section of the regionals (Oswestry, Kidderminster, Stoke, Coventry)? Wet n Dry selections please
Any other help g
ratefully received
Cheers
Lee