personally I diliske Wahsburn basses (guitars too but oh well), and yeah they're so cheap setting it up costs the same as buying it hahhaah
getting a 5 string or setting up a 4 string for B tuning is a matter of choice. There are many 4 stringers that come factory tuned very low (even F#), if you could get one of those it would be best for you cause obviously you won't be using the high G string, if you would you wouldn't bought a 4. Can't remember right now any specific ones, but search it, maybe on talkbass you could find some good info, that place is heaven for bassists