Pickup addition

I have a Squier 5 string jazz with a p- bass neck. I'd like to add pickups (specifically ones with 1/4" pole pieces) to make it two dual J-bass pickups with series/parallel options along with still being able to get the single-coils by themselves. I'd like to keep the stock pickups as I like them and considering adding the Aguliar 5-string hot pickups. I'm betting the Aguilars will be a fair bit louder than the stock pickups. Is there anything I need to consider in this project I have in mind- like maybe how these pups will interact with each other when both activated. Maybe one be so much louder than the other it could just cancel out the stock pickup and not sound like a dual jazz?
 
I recommend against doing what you have planned.

Challenges:
  • Hot J and normal J won't be balanced together. It won't hum cancel completely. The sound may or may not be what you are after.
  • A neck J is wound to hum cancel with a bridge J. Two neck J's won't hum cancel. And bridge J's are a little bit wider, so can't just put one up next to the neck pickup.
  • The pickups are not designed to mount right next to each other.
If you want a Jazz sound and other pickup sounds out of the same bass, I suggest getting humbuckers that can coil split. When you split them, combine north coil of neck with south coil of bridge to get the wider spacing. Humbucker mode will give you a hot sound. For the cost of the pickups you are considering, you can find a used Ibanez SR305E or Yamaha TRBX305. The basses are common, and you could find one to try in a music store.

An alternate pickup arrangement is to add a P pickup between the J pickups. That gives you a bunch of tone blend options. Be sure to have a cutoff switch for the P, and not just a blend. You can find circuit examples for JPJ.
 
I have a Squier 5 string jazz with a p- bass neck. I'd like to add pickups (specifically ones with 1/4" pole pieces) to make it two dual J-bass pickups with series/parallel options along with still being able to get the single-coils by themselves. I'd like to keep the stock pickups as I like them and considering adding the Aguliar 5-string hot pickups. I'm betting the Aguilars will be a fair bit louder than the stock pickups. Is there anything I need to consider in this project I have in mind- like maybe how these pups will interact with each other when both activated. Maybe one be so much louder than the other it could just cancel out the stock pickup and not sound like a dual jazz?
Why not buy off the shelf Dual Js ?
Delano,MEC, Fender Fireball etc.

You could buy a dual J cover and stick 2 Js of your choice underneath. ( 2 necks in the same cover / 2xbridge same cover)

The dissimilar pickups will NOT perform well at All! Together.

The 1/4 poles desired for what specifically?