When buying a bass, I would suggest getting a decent one used; it'll hold its value so if you decide to sell it you'll recoup your money and so it'll be a zero-cost item.
Of course, you'll get recommendation for a variety of instruments; I'd suggest looking at what your favourite musicians play and letting that steer your choice.
As far as playing goes, if you've done a bit of guitar, then you'll implicitly know where the notes are (ie. a 4-string bass is like the botton 4 strings of a guitar an octave lower).
A small clip-on tuner is a handy thing to have around (I have a Rotosound one, but there are plenty of brands about).