I have read now of for instance J-style basses, P-style basses...
How many 'styles' of bass are there, and what's the difference?

Maurits.

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there is tons of styles, and flat out they are all different. I would reccomend not buying a fender though. Mostly because they look atrocious in my opinion.
Basically a p bass is a precision bass and a j bass is a jazz bass, you figure it out.

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In P basses, the pickups are staggered

In J Basses, the pickups are in a straight line.

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its a little more complex than that, but thats still a good explanation.
on P-basses the pickups look like those stupid fucking staircase blocks in tetris that you can never use without fucking something else up. These are good for more vigorous playing like rock and metal etc...
the jazz pickups are a straight line, really narrow and have 2 magnets per string. These give a much more mellow and smooth tone, great for...well....jazz lol.
theres also pickups called "humbuckers" these are sort of a compromise, theyre alot more versatile in any field.

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those are passive pickups, right? or there are active J and P pickups too?

Usually the stock pickups are passive. But if you buy the higher priced basses they are sometimes active. Also, you can buy active Jazz and Precision pickups to replace the passive pickups in your bass if you want to... hell, you can buy almost ANY style of pickups that are active, from many manufacturers, such as Bartolini, Seymour Duncan, EMG... just to name a few.

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