Yes.
No, P-Bass pickups are not humbuckers. They are single-coil pickups commonly found on Precision Bass guitars.
There are many physical and online stores that sale bass pickups. Among them are Guitar Center, Upton Bass, Nordstran Pickups, Musicians Friend, and Talk Bass.
No, there is no such thing. The first Fender Jazz bass came with two pickups and that formula has been maintained to this day. The only "Jazz Bass" with one pickups is the Fender Mark Hoppus signature Jazz Bass, which comes with a single Precision Bass pickups. That particular bass sounds nothing like a standard Jazz Bass.
Most electric guitar and bass companies will have replacement pickups for fender basses. You can use any passive precision bass pickups to replace the ones found in your squier. Seymour Duncan always makes decent replacement pickups for a reasonable price. I've used many auction sites to procure lightly used or new pickups for repairs.
This arrangement reduces hum - much like when both pickups on the jazz bass are turned on.
Electromagnets are not used on bass guitars, but guitar and bass guitar pickups use magnets in order to turn the string's vibration into an electrical signal to send to amplifier.
The G10 has passive pickups. Active pickups require 9V batteries. No batteries required on the G10.
Not commonly. For drum and bass its best to use a loud, distinctive style of bass, for exaple i play alot of pendulum and use a Yamaha RBX 270. other good basses doe drum and bass are ones with Humbucker pickups - such as a fender Jazz Bass, or Ibanez
Using pick is not a matter of number of strings, it is rather a matter of personal preference or style of music you are playing. With a 4-string bass, you can use both pick and fingers.
Most have about 2 pick ups, but it depends since obviously like any other instrument they can be modified to have more or less. Usually a standard bass has 2 pick ups (P Style and J Style pick ups are popular and most pick ups are magnetic). A 5 or 6 string bass should have longer pick ups (wider) than a 4 string (shorts pick ups on 5 or 6 string basses yeild a poorer sound in most instances)
You can fingerpick using your....fingers or pick it using a plectrum/pick. Alternatively you can even pluck it or use a bow on something like a double bass.
usually pick for better quality sound but thumb can be used