I'll take a shot at breaking this down for you. Generally...chords consist of a root, a 3rd and 5th. You have identified all of these correctly. For a Bb chord they are Bb, D and F respectively. The A is the seventh and therefore you have 4 tones to complete this chord. Theoretically you are correct that the 2 F's are part of the chord sequence, but I would avoid both of the F's on the 1st and 6th strings due to tonalit. vidmate